# LazyList

scala.collection.immutable.LazyList
See theLazyList companion object
final class LazyList[+A] extends AbstractSeq[A],

This class implements an immutable linked list. We call it "lazy" because it computes its elements only when they are needed.

Elements are memoized; that is, the value of each element is computed at most once.

Elements are computed in-order and are never skipped. In other words, accessing the tail causes the head to be computed first.

How lazy is a LazyList? When you have a value of type LazyList, you don't know yet whether the list is empty or not. If you learn that it is non-empty, then you also know that the head has been computed. But the tail is itself a LazyList, whose emptiness-or-not might remain undetermined.

A LazyList may be infinite. For example, LazyList.from(0) contains all of the natural numbers 0, 1, 2, and so on. For infinite sequences, some methods (such as count, sum, max or min) will not terminate.

Here is an example:

import scala.math.BigInt
object Main extends App {
val fibs: LazyList[BigInt] =
BigInt(0) #:: BigInt(1) #:: fibs.zip(fibs.tail).map{ n => n._1 + n._2 }
fibs.take(5).foreach(println)
}

// prints
//
// 0
// 1
// 1
// 2
// 3

To illustrate, let's add some output to the definition fibs, so we see what's going on.

import scala.math.BigInt
object Main extends App {
val fibs: LazyList[BigInt] =
BigInt(0) #:: BigInt(1) #::
fibs.zip(fibs.tail).map{ n =>
n._1 + n._2
}
fibs.take(5).foreach(println)
fibs.take(6).foreach(println)
}

// prints
//
// 0
// 1
// 1
// 2
// 3

// And then prints
//
// 0
// 1
// 1
// 2
// 3
// 5

Note that the definition of fibs uses val not def. The memoization of the LazyList requires us to have somewhere to store the information and a val allows us to do that.

Further remarks about the semantics of LazyList:

- Though the LazyList changes as it is accessed, this does not contradict its immutability. Once the values are memoized they do not change. Values that have yet to be memoized still "exist", they simply haven't been computed yet.

- One must be cautious of memoization; it can eat up memory if you're not careful. That's because memoization of the LazyList creates a structure much like scala.collection.immutable.List. As long as something is holding on to the head, the head holds on to the tail, and so on recursively. If, on the other hand, there is nothing holding on to the head (e.g. if we used def to define the LazyList) then once it is no longer being used directly, it disappears.

- Note that some operations, including drop, dropWhile, flatMap or collect may process a large number of intermediate elements before returning.

Here's another example. Let's start with the natural numbers and iterate over them.

def loop(s: String, i: Int, iter: Iterator[Int]): Unit = {
// Stop after 200,000
if (i < 200001) {
if (i % 50000 == 0) println(s + i)
loop(s, iter.next(), iter)
}
}

// Our first LazyList definition will be a val definition
val lazylist1: LazyList[Int] = {
def loop(v: Int): LazyList[Int] = v #:: loop(v + 1)
loop(0)
}

// Because lazylist1 is a val, everything that the iterator produces is held
// by virtue of the fact that the head of the LazyList is held in lazylist1
val it1 = lazylist1.iterator
loop("Iterator1: ", it1.next(), it1)

// We can redefine this LazyList such that all we have is the Iterator left
// and allow the LazyList to be garbage collected as required.  Using a def
// to provide the LazyList ensures that no val is holding onto the head as
// is the case with lazylist1
def lazylist2: LazyList[Int] = {
def loop(v: Int): LazyList[Int] = v #:: loop(v + 1)
loop(0)
}
val it2 = lazylist2.iterator
loop("Iterator2: ", it2.next(), it2)

// And, of course, we don't actually need a LazyList at all for such a simple
// problem.  There's no reason to use a LazyList if you don't actually need
// one.
val it3 = new Iterator[Int] {
var i = -1
def hasNext = true
def next(): Int = { i += 1; i }
}
loop("Iterator3: ", it3.next(), it3)

- In the fibs example earlier, the fact that tail works at all is of interest. fibs has an initial (0, 1, LazyList(...)), so tail is deterministic. If we defined fibs such that only 0 were concretely known, then the act of determining tail would require the evaluation of tail, so the computation would be unable to progress, as in this code:

// The first time we try to access the tail we're going to need more
// information which will require us to recurse, which will require us to
// recurse, which...
lazy val sov: LazyList[Vector[Int]] = Vector(0) #:: sov.zip(sov.tail).map { n => n._1 ++ n._2 }

The definition of fibs above creates a larger number of objects than necessary depending on how you might want to implement it. The following implementation provides a more "cost effective" implementation due to the fact that it has a more direct route to the numbers themselves:

lazy val fib: LazyList[Int] = {
def loop(h: Int, n: Int): LazyList[Int] = h #:: loop(n, h + n)
loop(1, 1)
}

The head, the tail and whether the list is empty or not can be initially unknown. Once any of those are evaluated, they are all known, though if the tail is built with #:: or #:::, it's content still isn't evaluated. Instead, evaluating the tails content is deferred until the tails empty status, head or tail is evaluated.

Delaying the evaluation of whether a LazyList is empty or not until it's needed allows LazyList to not eagerly evaluate any elements on a call to filter.

Only when it's further evaluated (which may be never!) any of the elements gets forced.

for example:

def tailWithSideEffect: LazyList[Nothing] = {
println("getting empty LazyList")
LazyList.empty
}

val emptyTail = tailWithSideEffect // prints "getting empty LazyList"

val suspended = 1 #:: tailWithSideEffect // doesn't print anything
val tail = suspended.tail // although the tail is evaluated, *still* nothing is yet printed
val filtered = tail.filter(_ => false) // still nothing is printed
filtered.isEmpty // prints "getting empty LazyList"

## Type parameters

A

the type of the elements contained in this lazy list.

## Attributes

Companion
object
Source
LazyList.scala
Graph
Supertypes
trait Serializable
trait LinearSeq[A]
trait LinearSeq[A]
class AbstractSeq[A]
trait Seq[A]
trait SeqOps[A, LazyList, LazyList[A]]
trait Iterable[A]
class AbstractSeq[A]
trait Seq[A]
trait Equals
trait SeqOps[A, LazyList, LazyList[A]]
trait PartialFunction[Int, A]
trait Int => A
class AbstractIterable[A]
trait Iterable[A]
trait IterableOps[A, LazyList, LazyList[A]]
trait IterableOnce[A]
class Object
trait Matchable
class Any

## Members list

### Value members

#### Concrete methods

def #::[B >: A](elem: => B): LazyList[B]

Construct a LazyList consisting of a given first element followed by elements from another LazyList.

Construct a LazyList consisting of a given first element followed by elements from another LazyList.

## Attributes

Source
LazyList.scala
def #:::[B >: A](prefix: LazyList[B]): LazyList[B]

Construct a LazyList consisting of the concatenation of the given LazyList and another LazyList.

Construct a LazyList consisting of the concatenation of the given LazyList and another LazyList.

## Attributes

Source
LazyList.scala
override def addString(sb: StringBuilder, start: String, sep: String, end: String): sb.type

Appends all elements of this lazy list to a string builder using start, end, and separator strings.

Appends all elements of this lazy list to a string builder using start, end, and separator strings. The written text begins with the string start and ends with the string end. Inside, the string representations (w.r.t. the method toString) of all elements of this lazy list are separated by the string sep.

An undefined state is represented with "<not computed>" and cycles are represented with "<cycle>".

This method evaluates all elements of the collection.

## Value parameters

end

the ending string.

sb

the string builder to which elements are appended.

sep

the separator string.

start

the starting string.

## Attributes

Returns

the string builder b to which elements were appended.

Definition Classes
Source
LazyList.scala
override def appended[B >: A](elem: B): LazyList[B]

A copy of this lazy list with an element appended.

A copy of this lazy list with an element appended.

Note: will not terminate for infinite-sized collections.

Example:

scala> val a = List(1)
a: List[Int] = List(1)

scala> val b = a :+ 2
b: List[Int] = List(1, 2)

scala> println(a)
List(1)

This method preserves laziness; elements are only evaluated individually as needed.

Note: Repeated chaining of calls to append methods (appended, appendedAll, lazyAppendedAll) without forcing any of the intermediate resulting lazy lists may overflow the stack when the final result is forced.

## Attributes

Definition Classes
Source
LazyList.scala
override def appendedAll[B >: A](suffix: IterableOnce[B]): LazyList[B]

Returns a new lazy list containing the elements from the left hand operand followed by the elements from the right hand operand.

Returns a new lazy list containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the lazy list is the most specific superclass encompassing the element types of the two operands.

This method preserves laziness; elements are only evaluated individually as needed.

Note: Repeated chaining of calls to append methods (appended, appendedAll, lazyAppendedAll) without forcing any of the intermediate resulting lazy lists may overflow the stack when the final result is forced.

## Attributes

Definition Classes
Source
LazyList.scala
override def collect[B](pf: PartialFunction[A, B]): LazyList[B]

Builds a new lazy list by applying a partial function to all elements of this lazy list on which the function is defined.

Builds a new lazy list by applying a partial function to all elements of this lazy list on which the function is defined.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def collectFirst[B](pf: PartialFunction[A, B]): Option[B]

Finds the first element of the lazy list for which the given partial function is defined, and applies the partial function to it.

Finds the first element of the lazy list for which the given partial function is defined, and applies the partial function to it.

Note: may not terminate for infinite-sized collections.

This method does not evaluate any elements further than the first element for which the partial function is defined.

## Attributes

Definition Classes
Source
LazyList.scala
override def diff[B >: A](that: Seq[B]): LazyList[A]

Computes the multiset difference between this lazy list and another sequence.

Computes the multiset difference between this lazy list and another sequence.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def drop(n: Int): LazyList[A]

Selects all elements except the first n ones.

Selects all elements except the first n ones.

This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty). Additionally, it preserves laziness for all except the first n elements.

## Attributes

Definition Classes
Source
LazyList.scala
override def dropRight(n: Int): LazyList[A]

Selects all elements except last n ones.

Selects all elements except last n ones.

This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty).

## Attributes

Definition Classes
Source
LazyList.scala
override def dropWhile(p: A => Boolean): LazyList[A]

Selects all elements except the longest prefix that satisfies a predicate.

Selects all elements except the longest prefix that satisfies a predicate.

The matching prefix starts with the first element of this lazy list, and the element following the prefix is the first element that does not satisfy the predicate. The matching prefix may be empty, so that this method returns the entire lazy list.

Example:

scala> List(1, 2, 3, 100, 4).dropWhile(n => n < 10)
val res0: List[Int] = List(100, 4)

scala> List(1, 2, 3, 100, 4).dropWhile(n => n == 0)
val res1: List[Int] = List(1, 2, 3, 100, 4)

Use span to obtain both the prefix and suffix. Use filterNot to drop all elements that satisfy the predicate.

This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty). Additionally, it preserves laziness for all elements after the predicate returns false.

## Attributes

Definition Classes
Source
LazyList.scala
override def filter(pred: A => Boolean): LazyList[A]

Selects all elements of this lazy list which satisfy a predicate.

Selects all elements of this lazy list which satisfy a predicate.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def filterNot(pred: A => Boolean): LazyList[A]

Selects all elements of this lazy list which do not satisfy a predicate.

Selects all elements of this lazy list which do not satisfy a predicate.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def find(p: A => Boolean): Option[A]

Finds the first element of the lazy list satisfying a predicate, if any.

Finds the first element of the lazy list satisfying a predicate, if any.

Note: may not terminate for infinite-sized collections.

This method does not evaluate any elements further than the first element matching the predicate.

## Attributes

Definition Classes
Source
LazyList.scala
override def flatMap[B](f: A => IterableOnce[B]): LazyList[B]

Builds a new lazy list by applying a function to all elements of this lazy list and using the elements of the resulting collections.

Builds a new lazy list by applying a function to all elements of this lazy list and using the elements of the resulting collections.

For example:

def getWords(lines: Seq[String]): Seq[String] = lines flatMap (line => line split "\\W+")

The type of the resulting collection is guided by the static type of lazy list. This might cause unexpected results sometimes. For example:

// lettersOf will return a Seq[Char] of likely repeated letters, instead of a Set
def lettersOf(words: Seq[String]) = words flatMap (word => word.toSet)

// lettersOf will return a Set[Char], not a Seq
def lettersOf(words: Seq[String]) = words.toSet flatMap ((word: String) => word.toSeq)

// xs will be an Iterable[Int]
val xs = Map("a" -> List(11,111), "b" -> List(22,222)).flatMap(_._2)

// ys will be a Map[Int, Int]
val ys = Map("a" -> List(1 -> 11,1 -> 111), "b" -> List(2 -> 22,2 -> 222)).flatMap(_._2)

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def flatten[B](implicit asIterable: A => IterableOnce[B]): LazyList[B]

Converts this lazy list of iterable collections into a lazy list formed by the elements of these iterable collections.

Converts this lazy list of iterable collections into a lazy list formed by the elements of these iterable collections.

The resulting collection's type will be guided by the type of lazy list. For example:

val xs = List(
Set(1, 2, 3),
Set(1, 2, 3)
).flatten
// xs == List(1, 2, 3, 1, 2, 3)

val ys = Set(
List(1, 2, 3),
List(3, 2, 1)
).flatten
// ys == Set(1, 2, 3)

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def foldLeft[B](z: B)(op: (B, A) => B): B

LazyList specialization of foldLeft which allows GC to collect along the way.

LazyList specialization of foldLeft which allows GC to collect along the way.

## Type parameters

B

The type of value being accumulated.

## Value parameters

op

The operation to perform on successive elements of the LazyList.

z

The initial value seeded into the function op.

## Attributes

Returns

The accumulated value from successive applications of op.

Definition Classes
Source
LazyList.scala
def force: this.type

Evaluates all undefined elements of the lazy list.

Evaluates all undefined elements of the lazy list.

This method detects cycles in lazy lists, and terminates after all elements of the cycle are evaluated. For example:

val ring: LazyList[Int] = 1 #:: 2 #:: 3 #:: ring
ring.force
ring.toString

// prints
//
// LazyList(1, 2, 3, ...)

This method will *not* terminate for non-cyclic infinite-sized collections.

## Attributes

Returns

this

Source
LazyList.scala
override def foreach[U](f: A => U): Unit

Apply the given function f to each element of this linear sequence (while respecting the order of the elements).

Apply the given function f to each element of this linear sequence (while respecting the order of the elements).

## Value parameters

f

The treatment to apply to each element.

## Attributes

Note

Overridden here as final to trigger tail-call optimization, which replaces 'this' with 'tail' at each iteration. This is absolutely necessary for allowing the GC to collect the underlying LazyList as elements are consumed.

This function will force the realization of the entire LazyList unless the f throws an exception.

Definition Classes
Source
LazyList.scala
override def grouped(size: Int): Iterator[LazyList[A]]

Partitions elements in fixed size lazy lists.

Partitions elements in fixed size lazy lists.

The iterator returned by this method mostly preserves laziness; a single element ahead of the iterator is evaluated.

## Attributes

Definition Classes
Source
LazyList.scala

Selects the first element of this lazy list.

Selects the first element of this lazy list.

Note: *Must* be overridden in subclasses. The default implementation is inherited from IterableOps.

## Attributes

Definition Classes
Source
LazyList.scala
override def intersect[B >: A](that: Seq[B]): LazyList[A]

Computes the multiset intersection between this lazy list and another sequence.

Computes the multiset intersection between this lazy list and another sequence.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def isEmpty: Boolean

Tests whether the lazy list is empty.

Tests whether the lazy list is empty.

Note: The default implementation creates and discards an iterator.

Note: Implementations in subclasses that are not repeatedly iterable must take care not to consume any elements when isEmpty is called.

Note: *Must* be overridden in subclasses. The default implementation that is inherited from SeqOps uses lengthCompare, which is defined here to use isEmpty.

## Attributes

Definition Classes
Source
LazyList.scala

The companion object of this lazy list, providing various factory methods.

The companion object of this lazy list, providing various factory methods.

## Attributes

Note

When implementing a custom collection type and refining CC to the new type, this method needs to be overridden to return a factory for the new type (the compiler will issue an error otherwise).

Definition Classes
Source
LazyList.scala
override def iterator: Iterator[A]

An scala.collection.Iterator over the elements of this lazy list.

An scala.collection.Iterator over the elements of this lazy list.

If an IterableOnce object is in fact an scala.collection.Iterator, this method always returns itself, in its current state, but if it is an scala.collection.Iterable, this method always returns a new scala.collection.Iterator.

The iterator returned by this method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def knownSize: Int

The number of elements in this lazy list, if it can be cheaply computed, -1 otherwise.

The number of elements in this lazy list, if it can be cheaply computed, -1 otherwise. Cheaply usually means: Not requiring a collection traversal.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
def lazyAppendedAll[B >: A](suffix: => IterableOnce[B]): LazyList[B]

The lazy list resulting from the concatenation of this lazy list with the argument lazy list.

The lazy list resulting from the concatenation of this lazy list with the argument lazy list.

This method preserves laziness; elements are only evaluated individually as needed.

Note: Repeated chaining of calls to append methods (appended, appendedAll, lazyAppendedAll) without forcing any of the intermediate resulting lazy lists may overflow the stack when the final result is forced.

## Value parameters

suffix

The collection that gets appended to this lazy list

## Attributes

Returns

The lazy list containing elements of this lazy list and the iterable object.

Source
LazyList.scala
override def lazyZip[B](that: Iterable[B]): LazyZip2[A, B, this.type]

Analogous to zip except that the elements in each collection are not consumed until a strict operation is invoked on the returned LazyZip2 decorator.

Analogous to zip except that the elements in each collection are not consumed until a strict operation is invoked on the returned LazyZip2 decorator.

Calls to lazyZip can be chained to support higher arities (up to 4) without incurring the expense of constructing and deconstructing intermediary tuples.

val xs = List(1, 2, 3)
val res = (xs lazyZip xs lazyZip xs lazyZip xs).map((a, b, c, d) => a + b + c + d)
// res == List(4, 8, 12)

This method is not particularly useful for a lazy list, as zip already preserves laziness.

The collection.LazyZip2 returned by this method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def map[B](f: A => B): LazyList[B]

Builds a new lazy list by applying a function to all elements of this lazy list.

Builds a new lazy list by applying a function to all elements of this lazy list.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def padTo[B >: A](len: Int, elem: B): LazyList[B]

A copy of this lazy list with an element value appended until a given target length is reached.

A copy of this lazy list with an element value appended until a given target length is reached.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def partition(p: A => Boolean): (LazyList[A], LazyList[A])

A pair of, first, all elements that satisfy predicate p and, second, all elements that do not.

A pair of, first, all elements that satisfy predicate p and, second, all elements that do not. Interesting because it splits a collection in two.

The default implementation provided here needs to traverse the collection twice. Strict collections have an overridden version of partition in StrictOptimizedIterableOps, which requires only a single traversal.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def partitionMap[A1, A2](f: A => Either[A1, A2]): (LazyList[A1], LazyList[A2])

Applies a function f to each element of the lazy list and returns a pair of lazy lists: the first one made of those values returned by f that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.

Applies a function f to each element of the lazy list and returns a pair of lazy lists: the first one made of those values returned by f that were wrapped in scala.util.Left, and the second one made of those wrapped in scala.util.Right.

Example:

val xs = `LazyList`(1, "one", 2, "two", 3, "three") partitionMap {
case i: Int => Left(i)
case s: String => Right(s)
}
// xs == (`LazyList`(1, 2, 3),
//        `LazyList`(one, two, three))

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def patch[B >: A](from: Int, other: IterableOnce[B], replaced: Int): LazyList[B]

Produces a new lazy list where a slice of elements in this lazy list is replaced by another sequence.

Produces a new lazy list where a slice of elements in this lazy list is replaced by another sequence.

Patching at negative indices is the same as patching starting at 0. Patching at indices at or larger than the length of the original lazy list appends the patch to the end. If the replaced count would exceed the available elements, the difference in excess is ignored.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def prepended[B >: A](elem: B): LazyList[B]

A copy of the lazy list with an element prepended.

A copy of the lazy list with an element prepended.

Also, the original lazy list is not modified, so you will want to capture the result.

Example:

scala> val x = List(1)
x: List[Int] = List(1)

scala> val y = 2 +: x
y: List[Int] = List(2, 1)

scala> println(x)
List(1)

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def prependedAll[B >: A](prefix: IterableOnce[B]): LazyList[B]

As with :++, returns a new collection containing the elements from the left operand followed by the elements from the right operand.

As with :++, returns a new collection containing the elements from the left operand followed by the elements from the right operand.

It differs from :++ in that the right operand determines the type of the resulting collection rather than the left one. Mnemonic: the COLon is on the side of the new COLlection type.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def reduceLeft[B >: A](f: (B, A) => B): B

LazyList specialization of reduceLeft which allows GC to collect along the way.

LazyList specialization of reduceLeft which allows GC to collect along the way.

## Type parameters

B

The type of value being accumulated.

## Value parameters

f

The operation to perform on successive elements of the LazyList.

## Attributes

Returns

The accumulated value from successive applications of f.

Definition Classes
Source
LazyList.scala
override def reverse: LazyList[A]

Returns a new lazy list with the elements of this lazy list in reverse order.

Returns a new lazy list with the elements of this lazy list in reverse order.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

This method evaluates all elements of the collection.

## Attributes

Definition Classes
Source
LazyList.scala
override def scanLeft[B](z: B)(op: (B, A) => B): LazyList[B]

Produces a lazy list containing cumulative results of applying the operator going left to right, including the initial value.

Produces a lazy list containing cumulative results of applying the operator going left to right, including the initial value.

Note: will not terminate for infinite-sized collections.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def slice(from: Int, until: Int): LazyList[A]

Selects an interval of elements.

Selects an interval of elements. The returned lazy list is made up of all elements x which satisfy the invariant:

from <= indexOf(x) < until

This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty). Additionally, it preserves laziness for all but the first from elements.

## Attributes

Definition Classes
Source
LazyList.scala
override def sliding(size: Int, step: Int): Iterator[LazyList[A]]

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

The returned iterator will be empty when called on an empty collection. The last element the iterator produces may be smaller than the window size when the original collection isn't exhausted by the window before it and its last element isn't skipped by the step before it.

The iterator returned by this method mostly preserves laziness; size - step max 1 elements ahead of the iterator are evaluated.

## Attributes

Definition Classes
Source
LazyList.scala
override def tail: LazyList[A]

The rest of the collection without its first element.

The rest of the collection without its first element.

Note: *Must* be overridden in subclasses. The default implementation is inherited from IterableOps.

## Attributes

Definition Classes
Source
LazyList.scala
override def take(n: Int): LazyList[A]

Selects the first n elements.

Selects the first n elements.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def takeRight(n: Int): LazyList[A]

Selects the last n elements.

Selects the last n elements.

This method does not evaluate anything until an operation is performed on the result (e.g. calling head or tail, or checking if it is empty).

## Attributes

Definition Classes
Source
LazyList.scala
override def takeWhile(p: A => Boolean): LazyList[A]

Takes longest prefix of elements that satisfy a predicate.

Takes longest prefix of elements that satisfy a predicate.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def tapEach[U](f: A => U): LazyList[A]

Applies a side-effecting function to each element in this collection.

Applies a side-effecting function to each element in this collection. Strict collections will apply f to their elements immediately, while lazy collections like Views and LazyLists will only apply f on each element if and when that element is evaluated, and each time that element is evaluated.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def toString(): String

This method preserves laziness; elements are only evaluated individually as needed.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Returns

a string representation of this collection. An undefined state is represented with "<not computed>" and cycles are represented with "<cycle>" Examples:

• "LazyList(4, <not computed>)", a non-empty lazy list ;

• "LazyList(1, 2, 3, <not computed>)", a lazy list with at least three elements ;

• "LazyList(1, 2, 3, <cycle>)", an infinite lazy list that contains a cycle at the fourth element.

Definition Classes
Source
LazyList.scala
override def transpose[B](implicit asIterable: A => Iterable[B]): LazyList[LazyList[B]]

Transposes this lazy list of iterable collections into a lazy list of lazy lists.

Transposes this lazy list of iterable collections into a lazy list of lazy lists.

The resulting collection's type will be guided by the static type of lazy list. For example:

val xs = List(
Set(1, 2, 3),
Set(4, 5, 6)).transpose
// xs == List(
//         List(1, 4),
//         List(2, 5),
//         List(3, 6))

val ys = Vector(
List(1, 2, 3),
List(4, 5, 6)).transpose
// ys == Vector(
//         Vector(1, 4),
//         Vector(2, 5),
//         Vector(3, 6))

Note: Even when applied to a view or a lazy collection it will always force the elements.

This method evaluates all elements of the collection.

## Attributes

Definition Classes
Source
LazyList.scala
override def unzip[A1, A2](implicit asPair: A => (A1, A2)): (LazyList[A1], LazyList[A2])

Converts this lazy list of pairs into two collections of the first and second half of each pair.

Converts this lazy list of pairs into two collections of the first and second half of each pair.

val xs = `LazyList`(
(1, "one"),
(2, "two"),
(3, "three")).unzip
// xs == (`LazyList`(1, 2, 3),
//        `LazyList`(one, two, three))

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def unzip3[A1, A2, A3](implicit asTriple: A => (A1, A2, A3)): (LazyList[A1], LazyList[A2], LazyList[A3])

Converts this lazy list of triples into three collections of the first, second, and third element of each triple.

Converts this lazy list of triples into three collections of the first, second, and third element of each triple.

val xs = `LazyList`(
(1, "one", '1'),
(2, "two", '2'),
(3, "three", '3')).unzip3
// xs == (`LazyList`(1, 2, 3),
//        `LazyList`(one, two, three),
//        `LazyList`(1, 2, 3))

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def updated[B >: A](index: Int, elem: B): LazyList[B]

A copy of this lazy list with one single replaced element.

A copy of this lazy list with one single replaced element.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def withFilter(p: A => Boolean): WithFilter[A, LazyList]

A collection.WithFilter which allows GC of the head of lazy list during processing.

A collection.WithFilter which allows GC of the head of lazy list during processing.

This method is not particularly useful for a lazy list, as filter already preserves laziness.

The collection.WithFilter returned by this method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def zip[B](that: IterableOnce[B]): LazyList[(A, B)]

Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs.

Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs. If one of the two collections is longer than the other, its remaining elements are ignored.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def zipAll[A1 >: A, B](that: Iterable[B], thisElem: A1, thatElem: B): LazyList[(A1, B)]

Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs.

Returns a lazy list formed from this lazy list and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala
override def zipWithIndex: LazyList[(A, Int)]

Zips this lazy list with its indices.

Zips this lazy list with its indices.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Definition Classes
Source
LazyList.scala

#### Deprecated methods

override def hasDefiniteSize: Boolean

Tests whether this lazy list is known to have a finite size.

Tests whether this lazy list is known to have a finite size. All strict collections are known to have finite size. For a non-strict collection such as Stream, the predicate returns true if all elements have been computed. It returns false if the stream is not yet evaluated to the end. Non-empty Iterators usually return false even if they were created from a collection with a known finite size.

Note: many collection methods will not work on collections of infinite sizes. The typical failure mode is an infinite loop. These methods always attempt a traversal without checking first that hasDefiniteSize returns true. However, checking hasDefiniteSize can provide an assurance that size is well-defined and non-termination is not a concern.

This method preserves laziness; elements are only evaluated individually as needed.

## Attributes

Deprecated
true
Definition Classes
Source
LazyList.scala

#### Inherited methods

final def ++[B >: A](suffix: IterableOnce[B]): LazyList[B]

Alias for concat

Alias for concat

## Attributes

Inherited from:
IterableOps
Source
Iterable.scala
final override def ++:[B >: A](prefix: IterableOnce[B]): LazyList[B]

Alias for prependedAll.

Alias for prependedAll.

## Attributes

Definition Classes
Inherited from:
SeqOps
Source
Seq.scala
final def +:[B >: A](elem: B): LazyList[B]

Alias for prepended.

Alias for prepended.

Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.

## Attributes

Inherited from:
SeqOps
Source
Seq.scala
final def :+[B >: A](elem: B): LazyList[B]

Alias for appended.

Alias for appended.

Note that :-ending operators are right associative (see example). A mnemonic for +: vs. :+ is: the COLon goes on the COLlection side.

## Attributes

Inherited from:
SeqOps
Source
Seq.scala
final def :++[B >: A](suffix: IterableOnce[B]): LazyList[B]

Alias for appendedAll.

Alias for appendedAll.

## Attributes

Inherited from:
SeqOps
Source
Seq.scala

Appends all elements of this collection to a string builder.

Appends all elements of this collection to a string builder. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection without any separator string.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

h: StringBuilder = 1234

## Value parameters

b

the string builder to which elements are appended.

## Attributes

Returns

the string builder b to which elements were appended.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def addString(b: StringBuilder, sep: String): b.type

Appends all elements of this collection to a string builder using a separator string.

Appends all elements of this collection to a string builder using a separator string. The written text consists of the string representations (w.r.t. the method toString) of all elements of this collection, separated by the string sep.

Example:

scala> val a = List(1,2,3,4)
a: List[Int] = List(1, 2, 3, 4)

scala> val b = new StringBuilder()
b: StringBuilder =

res0: StringBuilder = 1, 2, 3, 4

## Value parameters

b

the string builder to which elements are appended.

sep

the separator string.

## Attributes

Returns

the string builder b to which elements were appended.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def andThen[C](k: PartialFunction[A, C]): PartialFunction[Int, C]

Composes this partial function with another partial function that gets applied to results of this partial function.

Composes this partial function with another partial function that gets applied to results of this partial function.

Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. For efficiency, it is recommended to call applyOrElse instead of isDefinedAt or apply.

## Type parameters

C

the result type of the transformation function.

## Value parameters

k

the transformation function

## Attributes

Returns

a partial function with the domain of this partial function narrowed by other partial function, which maps arguments x to k(this(x)).

Inherited from:
PartialFunction
Source
PartialFunction.scala
override def andThen[C](k: A => C): PartialFunction[Int, C]

Composes this partial function with a transformation function that gets applied to results of this partial function.

Composes this partial function with a transformation function that gets applied to results of this partial function.

If the runtime type of the function is a PartialFunction then the other andThen method is used (note its cautions).

## Type parameters

C

the result type of the transformation function.

## Value parameters

k

the transformation function

## Attributes

Returns

a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments x to k(this(x)).

Definition Classes
Inherited from:
PartialFunction
Source
PartialFunction.scala
override def apply(n: Int): A

Gets the element at the specified index.

Gets the element at the specified index. This operation is provided for convenience in Seq. It should not be assumed to be efficient unless you have an IndexedSeq.

## Attributes

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def applyOrElse[A1 <: Int, B1 >: A](x: A1, default: A1 => B1): B1

Applies this partial function to the given argument when it is contained in the function domain.

Applies this partial function to the given argument when it is contained in the function domain. Applies fallback function where this partial function is not defined.

Note that expression pf.applyOrElse(x, default) is equivalent to

if(pf isDefinedAt x) pf(x) else default(x)

except that applyOrElse method can be implemented more efficiently. For all partial function literals the compiler generates an applyOrElse implementation which avoids double evaluation of pattern matchers and guards. This makes applyOrElse the basis for the efficient implementation for many operations and scenarios, such as:

- combining partial functions into orElse/andThen chains does not lead to excessive apply/isDefinedAt evaluation - lift and unlift do not evaluate source functions twice on each invocation - runWith allows efficient imperative-style combining of partial functions with conditionally applied actions

For non-literal partial function classes with nontrivial isDefinedAt method it is recommended to override applyOrElse with custom implementation that avoids double isDefinedAt evaluation. This may result in better performance and more predictable behavior w.r.t. side effects.

## Value parameters

default

the fallback function

x

the function argument

## Attributes

Returns

the result of this function or fallback function application.

Inherited from:
PartialFunction
Source
PartialFunction.scala
def canEqual(that: Any): Boolean

Checks whether this instance can possibly equal that.

Checks whether this instance can possibly equal that.

A method that should be called from every well-designed equals method that is open to be overridden in a subclass. See Programming in Scala, Chapter 28 for discussion and design.

## Value parameters

that

the value being probed for possible equality

## Attributes

Returns

true if this instance can possibly equal that, otherwise false

Inherited from:
Seq
Source
Seq.scala

Iterates over combinations of elements.

Iterates over combinations of elements.

A combination of length n is a sequence of n elements selected in order of their first index in this sequence.

For example, "xyx" has two combinations of length 2. The x is selected first: "xx", "xy". The sequence "yx" is not returned as a combination because it is subsumed by "xy".

If there is more than one way to generate the same combination, only one will be returned.

For example, the result "xy" arbitrarily selected one of the x elements.

As a further illustration, "xyxx" has three different ways to generate "xy" because there are three elements x to choose from. Moreover, there are three unordered pairs "xx" but only one is returned.

It is not specified which of these equal combinations is returned. It is an implementation detail that should not be relied on. For example, the combination "xx" does not necessarily contain the first x in this sequence. This behavior is observable if the elements compare equal but are not identical.

As a consequence, "xyx".combinations(3).next() is "xxy": the combination does not reflect the order of the original sequence, but the order in which elements were selected, by "first index"; the order of each x element is also arbitrary.

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Attributes

Returns

An Iterator which traverses the n-element combinations of this sequence.

Example

Seq('a', 'b', 'b', 'b', 'c').combinations(2).foreach(println)
// List(a, b)
// List(a, c)
// List(b, b)
// List(b, c)
Seq('b', 'a', 'b').combinations(2).foreach(println)
// List(b, b)
// List(b, a)
Inherited from:
SeqOps
Source
Seq.scala
def compose[R](k: PartialFunction[R, Int]): PartialFunction[R, A]

Composes another partial function k with this partial function so that this partial function gets applied to results of k.

Composes another partial function k with this partial function so that this partial function gets applied to results of k.

Note that calling isDefinedAt on the resulting partial function may apply the first partial function and execute its side effect. For efficiency, it is recommended to call applyOrElse instead of isDefinedAt or apply.

## Type parameters

R

the parameter type of the transformation function.

## Value parameters

k

the transformation function

## Attributes

Returns

a partial function with the domain of other partial function narrowed by this partial function, which maps arguments x to this(k(x)).

Inherited from:
PartialFunction
Source
PartialFunction.scala
def compose[A](g: A => Int): A => A

Composes two instances of Function1 in a new Function1, with this function applied last.

Composes two instances of Function1 in a new Function1, with this function applied last.

## Type parameters

A

the type to which function g can be applied

## Value parameters

g

a function A => T1

## Attributes

Returns

a new function f such that f(x) == apply(g(x))

Inherited from:
Function1
Source
Function1.scala
final override def concat[B >: A](suffix: IterableOnce[B]): LazyList[B]

Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand.

Returns a new sequence containing the elements from the left hand operand followed by the elements from the right hand operand. The element type of the sequence is the most specific superclass encompassing the element types of the two operands.

## Type parameters

B

the element type of the returned collection.

## Value parameters

suffix

the iterable to append.

## Attributes

Returns

a new sequence which contains all elements of this sequence followed by all elements of suffix.

Definition Classes
Inherited from:
SeqOps
Source
Seq.scala
override def contains[A1 >: A](elem: A1): Boolean

Tests whether this sequence contains a given value as an element.

Tests whether this sequence contains a given value as an element.

Note: may not terminate for infinite-sized collections.

## Value parameters

elem

the element to test.

## Attributes

Returns

true if this sequence has an element that is equal (as determined by ==) to elem, false otherwise.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def containsSlice[B >: A](that: Seq[B]): Boolean

Tests whether this sequence contains a given sequence as a slice.

Tests whether this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

## Value parameters

that

the sequence to test

## Attributes

Returns

true if this sequence contains a slice with the same elements as that, otherwise false.

Inherited from:
SeqOps
Source
Seq.scala
def copyToArray[B >: A](xs: Array[B], start: Int, len: Int): Int

Copy elements to an array, returning the number of elements written.

Copy elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with at most len elements of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached, or len elements have been copied.

## Type parameters

B

the type of the elements of the array.

## Value parameters

len

the maximal number of elements to copy.

start

the starting index of xs.

xs

the array to fill.

## Attributes

Returns

the number of elements written to the array

Note

Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def copyToArray[B >: A](xs: Array[B], start: Int): Int

Copies elements to an array, returning the number of elements written.

Copies elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.

## Type parameters

B

the type of the elements of the array.

## Value parameters

start

the starting index of xs.

xs

the array to fill.

## Attributes

Returns

the number of elements written to the array

Note

Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def copyToArray[B >: A](xs: Array[B]): Int

Copies elements to an array, returning the number of elements written.

Copies elements to an array, returning the number of elements written.

Fills the given array xs starting at index start with values of this collection.

Copying will stop once either all the elements of this collection have been copied, or the end of the array is reached.

## Type parameters

B

the type of the elements of the array.

## Value parameters

xs

the array to fill.

## Attributes

Returns

the number of elements written to the array

Note

Reuse: After calling this method, one should discard the iterator it was called on. Using it is undefined and subject to change.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def corresponds[B](that: IterableOnce[B])(p: (A, B) => Boolean): Boolean

Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.

Tests whether every element of this collection's iterator relates to the corresponding element of another collection by satisfying a test predicate.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

the type of the elements of that

## Value parameters

p

the test predicate, which relates elements from both collections

that

the other collection

## Attributes

Returns

true if both collections have the same length and p(x, y) is true for all corresponding elements x of this iterator and y of that, otherwise false

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def corresponds[B](that: Seq[B])(p: (A, B) => Boolean): Boolean

Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.

Tests whether every element of this sequence relates to the corresponding element of another sequence by satisfying a test predicate.

## Type parameters

B

the type of the elements of that

## Value parameters

p

the test predicate, which relates elements from both sequences

that

the other sequence

## Attributes

Returns

true if both sequences have the same length and p(x, y) is true for all corresponding elements x of this sequence and y of that, otherwise false.

Inherited from:
SeqOps
Source
Seq.scala
def count(p: A => Boolean): Int

Counts the number of elements in the collection which satisfy a predicate.

Counts the number of elements in the collection which satisfy a predicate.

Note: will not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

the number of elements satisfying the predicate p.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def distinct: LazyList[A]

Selects all the elements of this sequence ignoring the duplicates.

Selects all the elements of this sequence ignoring the duplicates.

## Attributes

Returns

a new sequence consisting of all the elements of this sequence without duplicates.

Inherited from:
SeqOps
Source
Seq.scala
def distinctBy[B](f: A => B): LazyList[A]

Selects all the elements of this sequence ignoring the duplicates as determined by == after applying the transforming function f.

Selects all the elements of this sequence ignoring the duplicates as determined by == after applying the transforming function f.

## Type parameters

B

the type of the elements after being transformed by f

## Value parameters

f

The transforming function whose result is used to determine the uniqueness of each element

## Attributes

Returns

a new sequence consisting of all the elements of this sequence without duplicates.

Inherited from:
SeqOps
Source
Seq.scala

Returns an extractor object with a unapplySeq method, which extracts each element of a sequence data.

Returns an extractor object with a unapplySeq method, which extracts each element of a sequence data.

## Attributes

Example

val firstChar: String => Option[Char] = _.headOption
Seq("foo", "bar", "baz") match {
case firstChar.unlift.elementWise(c0, c1, c2) =>
println(s"\$c0, \$c1, \$c2") // Output: f, b, b
}
Inherited from:
PartialFunction
Source
PartialFunction.scala
override def empty: LazyList[A]

The empty iterable of the same type as this iterable

The empty iterable of the same type as this iterable

## Attributes

Returns

an empty iterable of type C.

Definition Classes
Inherited from:
IterableFactoryDefaults
Source
Iterable.scala
def endsWith[B >: A](that: Iterable[B]): Boolean

Tests whether this sequence ends with the given sequence.

Tests whether this sequence ends with the given sequence.

Note: will not terminate for infinite-sized collections.

## Value parameters

that

the sequence to test

## Attributes

Returns

true if this sequence has that as a suffix, false otherwise.

Inherited from:
SeqOps
Source
Seq.scala
override def equals(o: Any): Boolean

Checks whether this instance is equal to that.

Checks whether this instance is equal to that. This universal equality method is defined in AnyRef.

## Attributes

Definition Classes
Seq -> Equals -> Any
Inherited from:
Seq
Source
Seq.scala
override def exists(p: A => Boolean): Boolean

Tests whether a predicate holds for at least one element of this sequence.

Tests whether a predicate holds for at least one element of this sequence.

Note: may not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

true if the given predicate p is satisfied by at least one element of this sequence, otherwise false

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
override def findLast(p: A => Boolean): Option[A]

Finds the last element of the sequence satisfying a predicate, if any.

Finds the last element of the sequence satisfying a predicate, if any.

Note: will not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

an option value containing the last element in the sequence that satisfies p, or None if none exists.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def fold[A1 >: A](z: A1)(op: (A1, A1) => A1): A1

Applies the given binary operator op to the given initial value z and all elements of this collection.

Applies the given binary operator op to the given initial value z and all elements of this collection.

For each application of the operator, each operand is either an element of this collection, the initial value, or another such application of the operator.

The order of applications of the operator is unspecified and may be nondeterministic. Each element appears exactly once in the computation. The initial value may be used an arbitrary number of times, but at least once.

If this collection is ordered, then for any application of the operator, the element(s) appearing in the left operand will precede those in the right.

Note: might return different results for different runs, unless either of the following conditions is met: (1) the operator is associative, and the underlying collection type is ordered; or (2) the operator is associative and commutative. In either case, it is also necessary that the initial value be a neutral value for the operator, e.g. Nil for List concatenation or 1 for multiplication.

The default implementation in IterableOnce is equivalent to foldLeft but may be overridden for more efficient traversal orders.

Note: will not terminate for infinite-sized collections.

## Type parameters

A1

The type parameter for the binary operator, a supertype of A.

## Value parameters

op

A binary operator; must be associative for the result to always be the same across runs.

z

An initial value; may be used an arbitrary number of times in the computation of the result; must be a neutral value for op for the result to always be the same across runs.

## Attributes

Returns

The result of applying op between all the elements and z, or z if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def foldRight[B](z: B)(op: (A, B) => B): B

Applies the given binary operator op to all elements of this collection and the given initial value z, going right to left.

Applies the given binary operator op to all elements of this collection and the given initial value z, going right to left. Returns the initial value if this collection is empty.

"Going right to left" only makes sense if this collection is ordered: then if x1, x2, ..., xn are the elements of this collection, the result is op(x1, op(x2, op( ... op(xn, z) ... ))).

If this collection is not ordered, then for each application of the operator, each left operand is an element. In addition, the rightmost operand is the initial value, and each other right operand is itself an application of the operator. The elements of this collection and the initial value all appear exactly once in the computation.

Note: might return different results for different runs, unless the underlying collection type is ordered.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the binary operator.

## Value parameters

op

A binary operator.

z

An initial value.

## Attributes

Returns

The result of applying op to all elements of this collection and z, going right to left. Returns z if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
override def forall(p: A => Boolean): Boolean

Tests whether a predicate holds for all elements of this sequence.

Tests whether a predicate holds for all elements of this sequence.

Note: may not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

true if this sequence is empty or the given predicate p holds for all elements of this sequence, otherwise false.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
protected def fromSpecific(coll: IterableOnce[A]): LazyList[A]

Defines how to turn a given Iterable[A] into a collection of type C.

Defines how to turn a given Iterable[A] into a collection of type C.

This process can be done in a strict way or a non-strict way (ie. without evaluating the elements of the resulting collections). In other words, this methods defines the evaluation model of the collection.

## Attributes

Note

When implementing a custom collection type and refining C to the new type, this method needs to be overridden (the compiler will issue an error otherwise). In the common case where C =:= CC[A], this can be done by mixing in the scala.collection.IterableFactoryDefaults trait, which implements the method using iterableFactory.

As witnessed by the @uncheckedVariance annotation, using this method might be unsound. However, as long as it is called with an Iterable[A] obtained from this collection (as it is the case in the implementations of operations where we use a View[A]), it is safe.

Inherited from:
IterableFactoryDefaults
Source
Iterable.scala
def groupBy[K](f: A => K): Map[K, LazyList[A]]

Partitions this iterable collection into a map of iterable collections according to some discriminator function.

Partitions this iterable collection into a map of iterable collections according to some discriminator function.

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Type parameters

K

the type of keys returned by the discriminator function.

## Value parameters

f

the discriminator function.

## Attributes

Returns

A map from keys to iterable collections such that the following invariant holds:

(xs groupBy f)(k) = xs filter (x => f(x) == k)

That is, every key k is bound to a iterable collection of those elements x for which f(x) equals k.

Inherited from:
IterableOps
Source
Iterable.scala
def groupMap[K, B](key: A => K)(f: A => B): Map[K, LazyList[B]]

Partitions this iterable collection into a map of iterable collections according to a discriminator function key.

Partitions this iterable collection into a map of iterable collections according to a discriminator function key. Each element in a group is transformed into a value of type B using the value function.

It is equivalent to groupBy(key).mapValues(_.map(f)), but more efficient.

case class User(name: String, age: Int)

def namesByAge(users: Seq[User]): Map[Int, Seq[String]] =
users.groupMap(_.age)(_.name)

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Type parameters

B

the type of values returned by the transformation function

K

the type of keys returned by the discriminator function

## Value parameters

f

the element transformation function

key

the discriminator function

## Attributes

Inherited from:
IterableOps
Source
Iterable.scala
def groupMapReduce[K, B](key: A => K)(f: A => B)(reduce: (B, B) => B): Map[K, B]

Partitions this iterable collection into a map according to a discriminator function key.

Partitions this iterable collection into a map according to a discriminator function key. All the values that have the same discriminator are then transformed by the f function and then reduced into a single value with the reduce function.

It is equivalent to groupBy(key).mapValues(_.map(f).reduce(reduce)), but more efficient.

def occurrences[A](as: Seq[A]): Map[A, Int] =
as.groupMapReduce(identity)(_ => 1)(_ + _)

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Attributes

Inherited from:
IterableOps
Source
Iterable.scala
override def hashCode(): Int

Calculates a hash code value for the object.

Calculates a hash code value for the object.

The default hashing algorithm is platform dependent.

Note that it is allowed for two objects to have identical hash codes (o1.hashCode.equals(o2.hashCode)) yet not be equal (o1.equals(o2) returns false). A degenerate implementation could always return 0. However, it is required that if two objects are equal (o1.equals(o2) returns true) that they have identical hash codes (o1.hashCode.equals(o2.hashCode)). Therefore, when overriding this method, be sure to verify that the behavior is consistent with the equals method.

## Attributes

Returns

the hash code value for this object.

Definition Classes
Seq -> Any
Inherited from:
Seq
Source
Seq.scala

Optionally selects the first element.

Optionally selects the first element.

## Attributes

Returns

the first element of this sequence if it is nonempty, None if it is empty.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def indexOf[B >: A](elem: B): Int

Finds index of first occurrence of some value in this sequence.

Finds index of first occurrence of some value in this sequence.

## Type parameters

B

the type of the element elem.

## Value parameters

elem

the element value to search for.

## Attributes

Returns

the index >= 0 of the first element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.

Inherited from:
SeqOps
Source
Seq.scala
def indexOf[B >: A](elem: B, from: Int): Int

Finds index of first occurrence of some value in this sequence after or at some start index.

Finds index of first occurrence of some value in this sequence after or at some start index.

## Type parameters

B

the type of the element elem.

## Value parameters

elem

the element value to search for.

from

the start index

## Attributes

Returns

the index >= from of the first element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.

Inherited from:
SeqOps
Source
Seq.scala
def indexOfSlice[B >: A](that: Seq[B]): Int

Finds first index where this sequence contains a given sequence as a slice.

Finds first index where this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

## Value parameters

that

the sequence to test

## Attributes

Returns

the first index >= 0 such that the elements of this sequence starting at this index match the elements of sequence that, or -1 if no such subsequence exists.

Inherited from:
SeqOps
Source
Seq.scala
def indexOfSlice[B >: A](that: Seq[B], from: Int): Int

Finds first index after or at a start index where this sequence contains a given sequence as a slice.

Finds first index after or at a start index where this sequence contains a given sequence as a slice.

Note: may not terminate for infinite-sized collections.

## Value parameters

from

the start index

that

the sequence to test

## Attributes

Returns

the first index >= from such that the elements of this sequence starting at this index match the elements of sequence that, or -1 if no such subsequence exists.

Inherited from:
SeqOps
Source
Seq.scala
override def indexWhere(p: A => Boolean, from: Int): Int

Finds index of the first element satisfying some predicate after or at some start index.

Finds index of the first element satisfying some predicate after or at some start index.

Note: may not terminate for infinite-sized collections.

## Value parameters

from

the start index

p

the predicate used to test elements.

## Attributes

Returns

the index >= from of the first element of this sequence that satisfies the predicate p, or -1, if none exists.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def indexWhere(p: A => Boolean): Int

Finds index of the first element satisfying some predicate.

Finds index of the first element satisfying some predicate.

Note: may not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

the index >= 0 of the first element of this sequence that satisfies the predicate p, or -1, if none exists.

Inherited from:
SeqOps
Source
Seq.scala
def indices: Range

Produces the range of all indices of this sequence.

Produces the range of all indices of this sequence.

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Attributes

Returns

a Range value from 0 to one less than the length of this sequence.

Inherited from:
SeqOps
Source
Seq.scala
def init: LazyList[A]

The initial part of the collection without its last element.

The initial part of the collection without its last element.

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Attributes

Inherited from:
IterableOps
Source
Iterable.scala

Iterates over the inits of this iterable collection.

Iterates over the inits of this iterable collection. The first value will be this iterable collection and the final one will be an empty iterable collection, with the intervening values the results of successive applications of init.

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Attributes

Returns

an iterator over all the inits of this iterable collection

Example

List(1,2,3).inits = Iterator(List(1,2,3), List(1,2), List(1), Nil)

Inherited from:
IterableOps
Source
Iterable.scala
override def isDefinedAt(x: Int): Boolean

Tests whether this sequence contains given index.

Tests whether this sequence contains given index.

The implementations of methods apply and isDefinedAt turn a Seq[A] into a PartialFunction[Int, A].

## Value parameters

idx

the index to test

## Attributes

Returns

true if this sequence contains an element at position idx, false otherwise.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
override def isTraversableAgain: Boolean

Tests whether this iterable collection can be repeatedly traversed.

Tests whether this iterable collection can be repeatedly traversed. Always true for Iterables and false for Iterators unless overridden.

## Attributes

Returns

true if it is repeatedly traversable, false otherwise.

Definition Classes
Inherited from:
IterableOps
Source
Iterable.scala
override def last: A

Selects the last element.

Selects the last element.

## Attributes

Returns

The last element of this sequence.

Throws

NoSuchElementException If the sequence is empty.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def lastIndexOf[B >: A](elem: B, end: Int): Int

Finds index of last occurrence of some value in this sequence before or at a given end index.

Finds index of last occurrence of some value in this sequence before or at a given end index.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

the type of the element elem.

## Value parameters

elem

the element value to search for.

end

the end index.

## Attributes

Returns

the index <= end of the last element of this sequence that is equal (as determined by ==) to elem, or -1, if none exists.

Inherited from:
SeqOps
Source
Seq.scala
def lastIndexOfSlice[B >: A](that: Seq[B]): Int

Finds last index where this sequence contains a given sequence as a slice.

Finds last index where this sequence contains a given sequence as a slice.

Note: will not terminate for infinite-sized collections.

## Value parameters

that

the sequence to test

## Attributes

Returns

the last index such that the elements of this sequence starting at this index match the elements of sequence that, or -1 if no such subsequence exists.

Inherited from:
SeqOps
Source
Seq.scala
def lastIndexOfSlice[B >: A](that: Seq[B], end: Int): Int

Finds last index before or at a given end index where this sequence contains a given sequence as a slice.

Finds last index before or at a given end index where this sequence contains a given sequence as a slice.

Note: will not terminate for infinite-sized collections.

## Value parameters

end

the end index

that

the sequence to test

## Attributes

Returns

the last index <= end such that the elements of this sequence starting at this index match the elements of sequence that, or -1 if no such subsequence exists.

Inherited from:
SeqOps
Source
Seq.scala
override def lastIndexWhere(p: A => Boolean, end: Int): Int

Finds index of last element satisfying some predicate before or at given end index.

Finds index of last element satisfying some predicate before or at given end index.

Note: will not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

the index <= end of the last element of this sequence that satisfies the predicate p, or -1, if none exists.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def lastIndexWhere(p: A => Boolean): Int

Finds index of last element satisfying some predicate.

Finds index of last element satisfying some predicate.

Note: will not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

the index of the last element of this sequence that satisfies the predicate p, or -1, if none exists.

Inherited from:
SeqOps
Source
Seq.scala
def lastOption: Option[A]

Optionally selects the last element.

Optionally selects the last element.

Note: might return different results for different runs, unless the underlying collection type is ordered.

## Attributes

Returns

the last element of this iterable collection\$ if it is nonempty, None if it is empty.

Inherited from:
IterableOps
Source
Iterable.scala
def length: Int

The length (number of elements) of the sequence.

The length (number of elements) of the sequence. size is an alias for length in Seq collections.

## Attributes

Inherited from:
LinearSeqOps
Source
LinearSeq.scala
override def lengthCompare(that: Iterable[_]): Int

Compares the length of this sequence to the size of another Iterable.

Compares the length of this sequence to the size of another Iterable.

## Value parameters

that

the Iterable whose size is compared with this sequence's length.

## Attributes

Returns

A value x where

x <  0       if this.length <  that.size
x == 0       if this.length == that.size
x >  0       if this.length >  that.size

The method as implemented here does not call length or size directly; its running time is O(this.length min that.size) instead of O(this.length + that.size). The method should be overridden if computing size is cheap and knownSize returns -1.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
override def lengthCompare(len: Int): Int

Compares the length of this sequence to a test value.

Compares the length of this sequence to a test value.

## Value parameters

len

the test value that gets compared with the length.

## Attributes

Returns

A value x where

x <  0       if this.length <  len
x == 0       if this.length == len
x >  0       if this.length >  len

The method as implemented here does not call length directly; its running time is O(length min len) instead of O(length). The method should be overridden if computing length is cheap and knownSize returns -1.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala

Returns a value class containing operations for comparing the length of this sequence to a test value.

Returns a value class containing operations for comparing the length of this sequence to a test value.

These operations are implemented in terms of lengthCompare(Int), and allow the following more readable usages:

this.lengthIs < len     // this.lengthCompare(len) < 0
this.lengthIs <= len    // this.lengthCompare(len) <= 0
this.lengthIs == len    // this.lengthCompare(len) == 0
this.lengthIs != len    // this.lengthCompare(len) != 0
this.lengthIs >= len    // this.lengthCompare(len) >= 0
this.lengthIs > len     // this.lengthCompare(len) > 0

## Attributes

Inherited from:
SeqOps
Source
Seq.scala
def lift: Int => Option[A]

Turns this partial function into a plain function returning an Option result.

Turns this partial function into a plain function returning an Option result.

## Attributes

Returns

a function that takes an argument x to Some(this(x)) if this is defined for x, and to None otherwise.

Function.unlift

Inherited from:
PartialFunction
Source
PartialFunction.scala
def max[B >: A](implicit ord: Ordering[B]): A

Finds the largest element.

Finds the largest element.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The type over which the ordering is defined.

## Value parameters

ord

An ordering to be used for comparing elements.

## Attributes

Returns

the largest element of this collection with respect to the ordering ord.

Throws

UnsupportedOperationException if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def maxBy[B](f: A => B)(implicit ord: Ordering[B]): A

Finds the first element which yields the largest value measured by function f.

Finds the first element which yields the largest value measured by function f.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the function f.

## Value parameters

cmp

An ordering to be used for comparing elements.

f

The measuring function.

## Attributes

Returns

the first element of this collection with the largest value measured by function f with respect to the ordering cmp.

Throws

UnsupportedOperationException if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def maxByOption[B](f: A => B)(implicit ord: Ordering[B]): Option[A]

Finds the first element which yields the largest value measured by function f.

Finds the first element which yields the largest value measured by function f.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the function f.

## Value parameters

cmp

An ordering to be used for comparing elements.

f

The measuring function.

## Attributes

Returns

an option value containing the first element of this collection with the largest value measured by function f with respect to the ordering cmp.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def maxOption[B >: A](implicit ord: Ordering[B]): Option[A]

Finds the largest element.

Finds the largest element.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The type over which the ordering is defined.

## Value parameters

ord

An ordering to be used for comparing elements.

## Attributes

Returns

an option value containing the largest element of this collection with respect to the ordering ord.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def min[B >: A](implicit ord: Ordering[B]): A

Finds the smallest element.

Finds the smallest element.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The type over which the ordering is defined.

## Value parameters

ord

An ordering to be used for comparing elements.

## Attributes

Returns

the smallest element of this collection with respect to the ordering ord.

Throws

UnsupportedOperationException if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def minBy[B](f: A => B)(implicit ord: Ordering[B]): A

Finds the first element which yields the smallest value measured by function f.

Finds the first element which yields the smallest value measured by function f.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the function f.

## Value parameters

cmp

An ordering to be used for comparing elements.

f

The measuring function.

## Attributes

Returns

the first element of this collection with the smallest value measured by function f with respect to the ordering cmp.

Throws

UnsupportedOperationException if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def minByOption[B](f: A => B)(implicit ord: Ordering[B]): Option[A]

Finds the first element which yields the smallest value measured by function f.

Finds the first element which yields the smallest value measured by function f.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the function f.

## Value parameters

cmp

An ordering to be used for comparing elements.

f

The measuring function.

## Attributes

Returns

an option value containing the first element of this collection with the smallest value measured by function f with respect to the ordering cmp.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def minOption[B >: A](implicit ord: Ordering[B]): Option[A]

Finds the smallest element.

Finds the smallest element.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The type over which the ordering is defined.

## Value parameters

ord

An ordering to be used for comparing elements.

## Attributes

Returns

an option value containing the smallest element of this collection with respect to the ordering ord.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def mkString: String

Displays all elements of this collection in a string.

Displays all elements of this collection in a string.

Delegates to addString, which can be overridden.

## Attributes

Returns

a string representation of this collection. In the resulting string the string representations (w.r.t. the method toString) of all elements of this collection follow each other without any separator string.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def mkString(sep: String): String

Displays all elements of this collection in a string using a separator string.

Displays all elements of this collection in a string using a separator string.

Delegates to addString, which can be overridden.

## Value parameters

sep

the separator string.

## Attributes

Returns

a string representation of this collection. In the resulting string the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.

Example

List(1, 2, 3).mkString("|") = "1|2|3"

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def mkString(start: String, sep: String, end: String): String

Displays all elements of this collection in a string using start, end, and separator strings.

Displays all elements of this collection in a string using start, end, and separator strings.

Delegates to addString, which can be overridden.

## Value parameters

end

the ending string.

sep

the separator string.

start

the starting string.

## Attributes

Returns

a string representation of this collection. The resulting string begins with the string start and ends with the string end. Inside, the string representations (w.r.t. the method toString) of all elements of this collection are separated by the string sep.

Example

List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
protected def newSpecificBuilder: Builder[A, LazyList[A]]

## Attributes

Returns

a strict builder for the same collection type. Note that in the case of lazy collections (e.g. scala.collection.View or scala.collection.immutable.LazyList), it is possible to implement this method but the resulting Builder will break laziness. As a consequence, operations should preferably be implemented with fromSpecific instead of this method.

Note

When implementing a custom collection type and refining C to the new type, this method needs to be overridden (the compiler will issue an error otherwise). In the common case where C =:= CC[A], this can be done by mixing in the scala.collection.IterableFactoryDefaults trait, which implements the method using iterableFactory.

As witnessed by the @uncheckedVariance annotation, using this method might be unsound. However, as long as the returned builder is only fed with A values taken from this instance, it is safe.

Inherited from:
IterableFactoryDefaults
Source
Iterable.scala

Tests whether the collection is not empty.

Tests whether the collection is not empty.

## Attributes

Returns

true if the collection contains at least one element, false otherwise.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def orElse[A1 <: Int, B1 >: A](that: PartialFunction[A1, B1]): PartialFunction[A1, B1]

Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

Composes this partial function with a fallback partial function which gets applied where this partial function is not defined.

## Type parameters

A1

the argument type of the fallback function

B1

the result type of the fallback function

## Value parameters

that

the fallback function

## Attributes

Returns

a partial function which has as domain the union of the domains of this partial function and that. The resulting partial function takes x to this(x) where this is defined, and to that(x) where it is not.

Inherited from:
PartialFunction
Source
PartialFunction.scala

Iterates over distinct permutations of elements.

Iterates over distinct permutations of elements.

Note: Even when applied to a view or a lazy collection it will always force the elements.

## Attributes

Returns

An Iterator which traverses the distinct permutations of this sequence.

Example

Seq('a', 'b', 'b').permutations.foreach(println)
// List(a, b, b)
// List(b, a, b)
// List(b, b, a)
Inherited from:
SeqOps
Source
Seq.scala
def product[B >: A](implicit num: Numeric[B]): B

Multiplies together the elements of this collection.

Multiplies together the elements of this collection.

The default implementation uses reduce for a known non-empty collection, foldLeft otherwise.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

the result type of the * operator.

## Value parameters

num

an implicit parameter defining a set of numeric operations which includes the * operator to be used in forming the product.

## Attributes

Returns

the product of all elements of this collection with respect to the * operator in num.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def reduce[B >: A](op: (B, B) => B): B

Applies the given binary operator op to all elements of this collection.

Applies the given binary operator op to all elements of this collection.

For each application of the operator, each operand is either an element of this collection or another such application of the operator. The order of applications of the operator is unspecified and may be nondeterministic. Each element appears exactly once in the computation.

If this collection is ordered, then for any application of the operator, the element(s) appearing in the left operand will precede those in the right.

Note: might return different results for different runs, unless either of the following conditions is met: (1) the operator is associative, and the underlying collection type is ordered; or (2) the operator is associative and commutative.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The type parameter for the binary operator, a supertype of A.

## Value parameters

op

A binary operator; must be associative for the result to always be the same across runs.

## Attributes

Returns

The result of applying op between all the elements if the collection is nonempty.

Throws

UnsupportedOperationException if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def reduceLeftOption[B >: A](op: (B, A) => B): Option[B]

If this collection is nonempty, reduces it with the given binary operator op, going left to right.

If this collection is nonempty, reduces it with the given binary operator op, going left to right.

The behavior is the same as reduceLeft except that the value is None if the collection is empty. Each element appears exactly once in the computation.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the binary operator, a supertype of A.

## Value parameters

op

A binary operator.

## Attributes

Returns

The result of reducing this collection with op going left to right if the collection is nonempty, inside a Some, and None otherwise.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def reduceOption[B >: A](op: (B, B) => B): Option[B]

If this collection is nonempty, reduces it with the given binary operator op.

If this collection is nonempty, reduces it with the given binary operator op.

The behavior is the same as reduce except that the value is None if the collection is empty. The order of applications of the operator is unspecified and may be nondeterministic. Each element appears exactly once in the computation.

Note: might return different results for different runs, unless either of the following conditions is met: (1) the operator is associative, and the underlying collection type is ordered; or (2) the operator is associative and commutative.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

A type parameter for the binary operator, a supertype of A.

## Value parameters

op

A binary operator; must be associative for the result to always be the same across runs.

## Attributes

Returns

The result of reducing this collection with op if the collection is nonempty, inside a Some, and None otherwise.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def reduceRight[B >: A](op: (A, B) => B): B

Applies the given binary operator op to all elements of this collection, going right to left.

Applies the given binary operator op to all elements of this collection, going right to left.

"Going right to left" only makes sense if this collection is ordered: then if x1, x2, ..., xn are the elements of this collection, the result is op(x1, op(x2, op( ... op(xn-1, xn) ... ))).

If this collection is not ordered, then for each application of the operator, each left operand is an element. In addition, the rightmost operand is the last element of this collection and each other right operand is itself an application of the operator. Each element appears exactly once in the computation.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the binary operator, a supertype of A.

## Value parameters

op

A binary operator.

## Attributes

Returns

The result of applying op to all elements of this collection, going right to left.

Throws

UnsupportedOperationException if this collection is empty.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def reduceRightOption[B >: A](op: (A, B) => B): Option[B]

If this collection is nonempty, reduces it with the given binary operator op, going right to left.

If this collection is nonempty, reduces it with the given binary operator op, going right to left.

The behavior is the same as reduceRight except that the value is None if the collection is empty. Each element appears exactly once in the computation.

Note: might return different results for different runs, unless the underlying collection type is ordered or the operator is associative and commutative.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

The result type of the binary operator, a supertype of A.

## Value parameters

op

A binary operator.

## Attributes

Returns

The result of reducing this collection with op going right to left if the collection is nonempty, inside a Some, and None otherwise.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala

An iterator yielding the elements of this sequence in reverse order.

An iterator yielding the elements of this sequence in reverse order.

Note: will not terminate for infinite-sized collections.

Note: xs.reverseIterator is the same as xs.reverse.iterator but might be more efficient.

## Attributes

Returns

an iterator yielding the elements of this sequence in reverse order.

Inherited from:
SeqOps
Source
Seq.scala
protected def reversed: Iterable[A]

## Attributes

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def runWith[U](action: A => U): Int => Boolean

Composes this partial function with an action function which gets applied to results of this partial function.

Composes this partial function with an action function which gets applied to results of this partial function. The action function is invoked only for its side effects; its result is ignored.

Note that expression pf.runWith(action)(x) is equivalent to

if(pf isDefinedAt x) { action(pf(x)); true } else false

except that runWith is implemented via applyOrElse and thus potentially more efficient. Using runWith avoids double evaluation of pattern matchers and guards for partial function literals.

## Value parameters

action

the action function

## Attributes

Returns

a function which maps arguments x to isDefinedAt(x). The resulting function runs action(this(x)) where this is defined.

applyOrElse.

Inherited from:
PartialFunction
Source
PartialFunction.scala
override def sameElements[B >: A](that: IterableOnce[B]): Boolean

Tests whether the elements of this collection are the same (and in the same order) as those of that.

Tests whether the elements of this collection are the same (and in the same order) as those of that.

## Attributes

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def scan[B >: A](z: B)(op: (B, B) => B): LazyList[B]

Computes a prefix scan of the elements of the collection.

Computes a prefix scan of the elements of the collection.

Note: The neutral element z may be applied more than once.

## Type parameters

B

element type of the resulting collection

## Value parameters

op

the associative operator for the scan

z

neutral element for the operator op

## Attributes

Returns

a new iterable collection containing the prefix scan of the elements in this iterable collection

Inherited from:
IterableOps
Source
Iterable.scala
def scanRight[B](z: B)(op: (A, B) => B): LazyList[B]

Produces a collection containing cumulative results of applying the operator going right to left.

Produces a collection containing cumulative results of applying the operator going right to left. The head of the collection is the last cumulative result.

Note: will not terminate for infinite-sized collections.

Note: might return different results for different runs, unless the underlying collection type is ordered.

Note: Even when applied to a view or a lazy collection it will always force the elements.

Example:

List(1, 2, 3, 4).scanRight(0)(_ + _) == List(10, 9, 7, 4, 0)

## Type parameters

B

the type of the elements in the resulting collection

## Value parameters

op

the binary operator applied to the intermediate result and the element

z

the initial value

## Attributes

Returns

collection with intermediate results

Inherited from:
IterableOps
Source
Iterable.scala
def search[B >: A](elem: B, from: Int, to: Int)(implicit ord: Ordering[B]): SearchResult

Searches within an interval in this sorted sequence for a specific element.

Searches within an interval in this sorted sequence for a specific element. If this sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.

The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.

## Value parameters

elem

the element to find.

from

the index where the search starts.

ord

the ordering to be used to compare elements.

to

the index following where the search ends.

## Attributes

Returns

a Found value containing the index corresponding to the element in the sequence, or the InsertionPoint where the element would be inserted if the element is not in the sequence.

Note

if to <= from, the search space is empty, and an InsertionPoint at from is returned

Inherited from:
SeqOps
Source
Seq.scala
def search[B >: A](elem: B)(implicit ord: Ordering[B]): SearchResult

Searches this sorted sequence for a specific element.

Searches this sorted sequence for a specific element. If the sequence is an IndexedSeq, a binary search is used. Otherwise, a linear search is used.

The sequence should be sorted with the same Ordering before calling; otherwise, the results are undefined.

## Value parameters

elem

the element to find.

ord

the ordering to be used to compare elements.

## Attributes

Returns

a Found value containing the index corresponding to the element in the sequence, or the InsertionPoint where the element would be inserted if the element is not in the sequence.

Inherited from:
SeqOps
Source
Seq.scala
override def segmentLength(p: A => Boolean, from: Int): Int

Computes the length of the longest segment that starts from some index and whose elements all satisfy some predicate.

Computes the length of the longest segment that starts from some index and whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

## Value parameters

from

the index where the search starts.

p

the predicate used to test elements.

## Attributes

Returns

the length of the longest segment of this sequence starting from index from such that every element of the segment satisfies the predicate p.

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
final def segmentLength(p: A => Boolean): Int

Computes the length of the longest segment that starts from the first element and whose elements all satisfy some predicate.

Computes the length of the longest segment that starts from the first element and whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

the length of the longest segment of this sequence that starts from the first element such that every element of the segment satisfies the predicate p.

Inherited from:
SeqOps
Source
Seq.scala
final override def size: Int

The size of this sequence.

The size of this sequence.

Note: will not terminate for infinite-sized collections.

## Attributes

Returns

the number of elements in this sequence.

Definition Classes
Inherited from:
SeqOps
Source
Seq.scala
final override def sizeCompare(that: Iterable[_]): Int

Compares the size of this sequence to the size of another Iterable.

Compares the size of this sequence to the size of another Iterable.

## Value parameters

that

the Iterable whose size is compared with this sequence's size.

## Attributes

Returns

A value x where

x <  0       if this.size <  that.size
x == 0       if this.size == that.size
x >  0       if this.size >  that.size

The method as implemented here does not call size directly; its running time is O(this.size min that.size) instead of O(this.size + that.size). The method should be overridden if computing size is cheap and knownSize returns -1.

Definition Classes
Inherited from:
SeqOps
Source
Seq.scala
final override def sizeCompare(otherSize: Int): Int

Compares the size of this sequence to a test value.

Compares the size of this sequence to a test value.

## Value parameters

otherSize

the test value that gets compared with the size.

## Attributes

Returns

A value x where

x <  0       if this.size <  otherSize
x == 0       if this.size == otherSize
x >  0       if this.size >  otherSize

The method as implemented here does not call size directly; its running time is O(size min otherSize) instead of O(size). The method should be overridden if computing size is cheap and knownSize returns -1.

Definition Classes
Inherited from:
SeqOps
Source
Seq.scala
final def sizeIs: SizeCompareOps

Returns a value class containing operations for comparing the size of this iterable collection to a test value.

Returns a value class containing operations for comparing the size of this iterable collection to a test value.

These operations are implemented in terms of sizeCompare(Int), and allow the following more readable usages:

this.sizeIs < size     // this.sizeCompare(size) < 0
this.sizeIs <= size    // this.sizeCompare(size) <= 0
this.sizeIs == size    // this.sizeCompare(size) == 0
this.sizeIs != size    // this.sizeCompare(size) != 0
this.sizeIs >= size    // this.sizeCompare(size) >= 0
this.sizeIs > size     // this.sizeCompare(size) > 0

## Attributes

Inherited from:
IterableOps
Source
Iterable.scala
def sliding(size: Int): Iterator[LazyList[A]]

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

Groups elements in fixed size blocks by passing a "sliding window" over them (as opposed to partitioning them, as is done in grouped.)

An empty collection returns an empty iterator, and a non-empty collection containing fewer elements than the window size returns an iterator that will produce the original collection as its only element.

## Value parameters

size

the number of elements per group

## Attributes

Returns

An iterator producing iterable collections of size size, except for a non-empty collection with less than size elements, which returns an iterator that produces the source collection itself as its only element.

scala.collection.Iterator, method sliding

Example

List().sliding(2) = empty iterator

List(1).sliding(2) = Iterator(List(1))

List(1, 2).sliding(2) = Iterator(List(1, 2))

List(1, 2, 3).sliding(2) = Iterator(List(1, 2), List(2, 3))

Inherited from:
IterableOps
Source
Iterable.scala
def sortBy[B](f: A => B)(implicit ord: Ordering[B]): LazyList[A]

Sorts this sequence according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.

Sorts this sequence according to the Ordering which results from transforming an implicitly given Ordering with a transformation function.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.

## Type parameters

B

the target type of the transformation f, and the type where the ordering ord is defined.

## Value parameters

f

the transformation function mapping elements to some other domain B.

ord

the ordering assumed on domain B.

## Attributes

Returns

a sequence consisting of the elements of this sequence sorted according to the ordering where x < y if ord.lt(f(x), f(y)).

Example

val words = "The quick brown fox jumped over the lazy dog".split(' ')
// this works because scala.Ordering will implicitly provide an Ordering[Tuple2[Int, Char]]
res0: Array[String] = Array(The, dog, fox, the, lazy, over, brown, quick, jumped)
Inherited from:
SeqOps
Source
Seq.scala
def sortWith(lt: (A, A) => Boolean): LazyList[A]

Sorts this sequence according to a comparison function.

Sorts this sequence according to a comparison function.

Note: will not terminate for infinite-sized collections.

Note: Even when applied to a view or a lazy collection it will always force the elements.

The sort is stable. That is, elements that are equal (lt returns false for both directions of comparison) appear in the same order in the sorted sequence as in the original.

## Value parameters

lt

a predicate that is true if its first argument strictly precedes its second argument in the desired ordering.

## Attributes

Returns

a sequence consisting of the elements of this sequence sorted according to the comparison function lt.

Example

List("Steve", "Bobby", "Tom", "John", "Bob").sortWith((x, y) => x.take(3).compareTo(y.take(3)) < 0) =
List("Bobby", "Bob", "John", "Steve", "Tom")
Inherited from:
SeqOps
Source
Seq.scala
def sorted[B >: A](implicit ord: Ordering[B]): LazyList[A]

Sorts this sequence according to an Ordering.

Sorts this sequence according to an Ordering.

The sort is stable. That is, elements that are equal (as determined by ord.compare) appear in the same order in the sorted sequence as in the original.

## Value parameters

ord

the ordering to be used to compare elements.

## Attributes

Returns

a sequence consisting of the elements of this sequence sorted according to the ordering ord.

scala.math.Ordering Note: Even when applied to a view or a lazy collection it will always force the elements.

Inherited from:
SeqOps
Source
Seq.scala
def span(p: A => Boolean): (LazyList[A], LazyList[A])

Splits this iterable collection into a prefix/suffix pair according to a predicate.

Splits this iterable collection into a prefix/suffix pair according to a predicate.

Note: c span p is equivalent to (but possibly more efficient than) (c takeWhile p, c dropWhile p), provided the evaluation of the predicate p does not cause any side-effects.

Note: might return different results for different runs, unless the underlying collection type is ordered.

## Value parameters

p

the test predicate

## Attributes

Returns

a pair consisting of the longest prefix of this iterable collection whose elements all satisfy p, and the rest of this iterable collection.

Inherited from:
IterableOps
Source
Iterable.scala
override def splitAt(n: Int): (LazyList[A], LazyList[A])

Splits this iterable collection into a prefix/suffix pair at a given position.

Splits this iterable collection into a prefix/suffix pair at a given position.

Note: c splitAt n is equivalent to (but possibly more efficient than) (c take n, c drop n).

Note: might return different results for different runs, unless the underlying collection type is ordered.

## Value parameters

n

the position at which to split.

## Attributes

Returns

a pair of iterable collections consisting of the first n elements of this iterable collection, and the other elements.

Definition Classes
Inherited from:
IterableOps
Source
Iterable.scala
def startsWith[B >: A](that: IterableOnce[B], offset: Int): Boolean

Tests whether this sequence contains the given sequence at a given index.

Tests whether this sequence contains the given sequence at a given index.

Note: If the both the receiver object this and the argument that are infinite sequences this method may not terminate.

## Value parameters

offset

the index where the sequence is searched.

that

the sequence to test

## Attributes

Returns

true if the sequence that is contained in this sequence at index offset, otherwise false.

Inherited from:
SeqOps
Source
Seq.scala
def stepper[S <: Stepper[_]](implicit shape: StepperShape[A, S]): S

Returns a scala.collection.Stepper for the elements of this collection.

Returns a scala.collection.Stepper for the elements of this collection.

The Stepper enables creating a Java stream to operate on the collection, see scala.jdk.StreamConverters. For collections holding primitive values, the Stepper can be used as an iterator which doesn't box the elements.

The implicit scala.collection.StepperShape parameter defines the resulting Stepper type according to the element type of this collection.

Note that this method is overridden in subclasses and the return type is refined to S with EfficientSplit, for example scala.collection.IndexedSeqOps.stepper. For Steppers marked with scala.collection.Stepper.EfficientSplit, the converters in scala.jdk.StreamConverters allow creating parallel streams, whereas bare Steppers can be converted only to sequential streams.

## Attributes

Inherited from:
IterableOnce
Source
IterableOnce.scala
def sum[B >: A](implicit num: Numeric[B]): B

Sums the elements of this collection.

Sums the elements of this collection.

The default implementation uses reduce for a known non-empty collection, foldLeft otherwise.

Note: will not terminate for infinite-sized collections.

## Type parameters

B

the result type of the + operator.

## Value parameters

num

an implicit parameter defining a set of numeric operations which includes the + operator to be used in forming the sum.

## Attributes

Returns

the sum of all elements of this collection with respect to the + operator in num.

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
override def tails: Iterator[LazyList[A]]

Iterates over the tails of this sequence.

Iterates over the tails of this sequence. The first value will be this sequence and the final one will be an empty sequence, with the intervening values the results of successive applications of tail.

## Attributes

Returns

an iterator over all the tails of this sequence

Example

List(1,2,3).tails = Iterator(List(1,2,3), List(2,3), List(3), Nil)

Definition Classes
Inherited from:
LinearSeqOps
Source
LinearSeq.scala
def to[C1](factory: Factory[A, C1]): C1

Given a collection factory factory, converts this collection to the appropriate representation for the current element type A.

Given a collection factory factory, converts this collection to the appropriate representation for the current element type A. Example uses:

xs.to(List)
xs.to(ArrayBuffer)
xs.to(BitSet) // for xs: Iterable[Int]

## Attributes

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def toArray[B >: A : ClassTag]: Array[B]

Converts this collection to an Array.

Converts this collection to an Array.

Implementation note: DO NOT call Array.from from this method.

## Type parameters

B

The type of elements of the result, a supertype of A.

## Attributes

Returns

This collection as an Array[B].

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def toBuffer[B >: A]: Buffer[B]

Converts this collection to a Buffer.

Converts this collection to a Buffer.

## Type parameters

B

The type of elements of the result, a supertype of A.

## Attributes

Returns

This collection as a Buffer[B].

Inherited from:
IterableOnceOps
Source
IterableOnce.scala

Converts this collection to an IndexedSeq.

Converts this collection to an IndexedSeq.

## Attributes

Returns

This collection as an IndexedSeq[A].

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def toList: List[A]

Converts this collection to a List.

Converts this collection to a List.

## Attributes

Returns

This collection as a List[A].

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def toMap[K, V](implicit ev: A <:< (K, V)): Map[K, V]

Converts this collection to a Map, given an implicit coercion from the collection's type to a key-value tuple.

Converts this collection to a Map, given an implicit coercion from the collection's type to a key-value tuple.

## Type parameters

K

The key type for the resulting map.

V

The value type for the resulting map.

## Value parameters

ev

An implicit coercion from A to [K, V].

## Attributes

Returns

This collection as a Map[K, V].

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final override def toSeq: Seq.this.type

## Attributes

Returns

This sequence as a Seq[A]. This is equivalent to to(Seq) but might be faster.

Definition Classes
Inherited from:
Seq
Source
Seq.scala
def toSet[B >: A]: Set[B]

Converts this collection to a Set.

Converts this collection to a Set.

## Type parameters

B

The type of elements of the result, a supertype of A.

## Attributes

Returns

This collection as a Set[B].

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def toVector: Vector[A]

Converts this collection to a Vector.

Converts this collection to a Vector.

## Attributes

Returns

This collection as a Vector[A].

Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def unapply(a: Int): Option[A]

Tries to extract a B from an A in a pattern matching expression.

Tries to extract a B from an A in a pattern matching expression.

## Attributes

Inherited from:
PartialFunction
Source
PartialFunction.scala
override def view: SeqView[A]

A view over the elements of this collection.

A view over the elements of this collection.

## Attributes

Definition Classes
Inherited from:
SeqOps
Source
Seq.scala

#### Deprecated and Inherited methods

final def /:[B](z: B)(op: (B, A) => B): B

## Attributes

Deprecated
true
Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def :\[B](z: B)(op: (A, B) => B): B

## Attributes

Deprecated
true
Inherited from:
IterableOnceOps
Source
IterableOnce.scala
def aggregate[B](z: => B)(seqop: (B, A) => B, combop: (B, B) => B): B

Aggregates the results of applying an operator to subsequent elements.

Aggregates the results of applying an operator to subsequent elements.

Since this method degenerates to foldLeft for sequential (non-parallel) collections, where the combining operation is ignored, it is advisable to prefer foldLeft for that case.

For parallel collections, use the aggregate method specified by scala.collection.parallel.ParIterableLike.

## Type parameters

B

the result type, produced by seqop, combop, and by this function as a final result.

## Value parameters

combop

an associative operator for combining sequential results, unused for sequential collections.

seqop

the binary operator used to accumulate the result.

z

the start value, a neutral element for seqop.

## Attributes

Deprecated
true
Inherited from:
IterableOnceOps
Source
IterableOnce.scala

## Attributes

Deprecated
true
Inherited from:
IterableOps
Source
Iterable.scala
final def copyToBuffer[B >: A](dest: Buffer[B]): Unit

## Attributes

Deprecated
true
Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def prefixLength(p: A => Boolean): Int

Returns the length of the longest prefix whose elements all satisfy some predicate.

Returns the length of the longest prefix whose elements all satisfy some predicate.

Note: may not terminate for infinite-sized collections.

## Value parameters

p

the predicate used to test elements.

## Attributes

Returns

the length of the longest prefix of this sequence such that every element of the segment satisfies the predicate p.

Deprecated
true
Inherited from:
SeqOps
Source
Seq.scala
final def repr: LazyList[A]

## Attributes

Deprecated
true
Inherited from:
IterableOps
Source
Iterable.scala
def reverseMap[B](f: A => B): LazyList[B]

## Attributes

Deprecated
true
Inherited from:
SeqOps
Source
Seq.scala
def seq: Iterable.this.type

## Attributes

Deprecated
true
Inherited from:
Iterable
Source
Iterable.scala
final def toIterable: Iterable.this.type

## Attributes

Returns

This collection as an Iterable[A]. No new collection will be built if this is already an Iterable[A].

Deprecated
true
Inherited from:
Iterable
Source
Iterable.scala
final def toIterator: Iterator[A]

## Attributes

Deprecated
true
Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def toStream: Stream[A]

## Attributes

Deprecated
true
Inherited from:
IterableOnceOps
Source
IterableOnce.scala
final def toTraversable: Iterable[A]

Converts this iterable collection to an unspecified Iterable.

Converts this iterable collection to an unspecified Iterable. Will return the same collection if this instance is already Iterable.

## Attributes

Returns

An Iterable containing all elements of this iterable collection.

Deprecated
true
Inherited from:
IterableOps
Source
Iterable.scala
final def union[B >: A](that: Seq[B]): LazyList[B]

Produces a new sequence which contains all elements of this sequence and also all elements of a given sequence.

Produces a new sequence which contains all elements of this sequence and also all elements of a given sequence. xs union ys is equivalent to xs ++ ys.

## Type parameters

B

the element type of the returned sequence.

that

## Attributes

Returns

a new collection which contains all elements of this sequence followed by all elements of that.

Deprecated
true
Inherited from:
SeqOps
Source
Seq.scala
def view(from: Int, until: Int): View[A]

A view over a slice of the elements of this collection.

A view over a slice of the elements of this collection.

Deprecated
true
Inherited from:
IterableOps
Source
Iterable.scala