List
@SerialVersionUID(3L) sealed abstract class List[+A] extends AbstractSeq[A] with LinearSeq[A] with LinearSeqOps[A, [A] =>> List[A], List[A]] with StrictOptimizedLinearSeqOps[A, [A] =>> List[A], List[A]] with StrictOptimizedSeqOps[A, [A] =>> List[A], List[A]] with IterableFactoryDefaults[A, [A] =>> List[A]] with DefaultSerializable
A class for immutable linked lists representing ordered collections
of elements of type
A
.This class comes with two implementing case classes
scala.Nil
and scala.::
that implement the abstract members isEmpty
,
head
and tail
.This class is optimal for last-in-first-out (LIFO), stack-like access patterns. If you need another access
pattern, for example, random access or FIFO, consider using a collection more suited to this than
List
.Performance
Time:
List
has O(1)
prepend and head/tail access. Most other operations are O(n)
on the number of elements in the list.
This includes the index-based lookup of elements, length
, append
and reverse
.Space:
List
implements structural sharing of the tail list. This means that many operations are either
zero- or constant-memory cost.val mainList = List(3, 2, 1)
val with4 = 4 :: mainList // re-uses mainList, costs one :: instance
val with42 = 42 :: mainList // also re-uses mainList, cost one :: instance
val shorter = mainList.tail // costs nothing as it uses the same 2::1::Nil instances as mainList
- See also
- "Scala's Collection Library overview" section on
Lists
for more information. - Note
- The functional list is characterized by persistence and structural sharing, thus offering considerable performance and space consumption benefits in some scenarios if used correctly. However, note that objects having multiple references into the same functional list (that is, objects that rely on structural sharing), will be serialized and deserialized with multiple lists, one for each reference to it. I.e. structural sharing is lost after serialization/deserialization.
- Example
// Make a list via the companion object factory val days = List("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday") // Make a list element-by-element val when = "AM" :: "PM" :: Nil // Pattern match days match { case firstDay :: otherDays => println("The first day of the week is: " + firstDay) case Nil => println("There don't seem to be any week days.") }
- Companion
- object
- Source
- (source)
trait DefaultSerializable
trait Serializable
class AbstractSeq[A]
class AbstractSeq[A]
trait Equals
class AbstractIterable[A]
trait IterableOnce[A]
class Object
trait Matchable
class Any
Value members
Methods
Adds an element at the beginning of this list.
- Value Params
- elem
-
the element to prepend.
- Returns
-
a list which contains
x
as first element and which continues with this list. Example:1 :: List(2, 3) = List(2, 3).::(1) = List(1, 2, 3)
- Source
- (source)
Adds the elements of a given list in front of this list.
Example:
List(1, 2) ::: List(3, 4) = List(3, 4).:::(List(1, 2)) = List(1, 2, 3, 4)
- Value Params
- prefix
-
The list elements to prepend.
- Returns
-
a list resulting from the concatenation of the given list
prefix
and this list. - Source
- (source)
Adds the elements of a given list in reverse order in front of this list.
xs reverse_::: ys
is equivalent to
xs.reverse ::: ys
but is more efficient.
- Value Params
- prefix
-
the prefix to reverse and then prepend
- Returns
-
the concatenation of the reversed prefix and the current list.
- Source
- (source)
- Example
// Given a list val letters = List('a','b','c','d','e') // `slice` returns all elements beginning at index `from` and afterwards, // up until index `until` (excluding index `until`.) letters.slice(1,3) // Returns List('b','c')
- Definition Classes
- Source
- (source)
- Definition Classes
- Source
- (source)
- Definition Classes
- Source
- (source)
- Definition Classes
- Source
- (source)
Builds a new list by applying a function to all elements of this list.
Like
xs map f
, but returns xs
unchanged if function
f
maps all elements to themselves (as determined by eq
).
- Type Params
- B
-
the element type of the returned collection.
- Value Params
- f
-
the function to apply to each element.
- Returns
-
a list resulting from applying the given function
f
to each element of this list and collecting the results. - Source
- (source)
Inherited methods
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.
Optionally applies a binary operator to all elements of this collection, going
right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the
underlying collection type is ordered or the operator is associative
and commutative.
- Type Params
- B
-
the result type of the binary operator.
- Value Params
- op
-
the binary operator.
- Returns
-
an option value containing the result of
reduceRight(op)
if this collection is nonempty,None
otherwise. - Inhertied from
- IterableOnceOps
- Source
- (source)
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 toif(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 Params
- action
-
the action function
- Returns
-
a function which maps arguments
x
toisDefinedAt(x)
. The resulting function runsaction(this(x))
wherethis
is defined. - See also
applyOrElse
.- Inhertied from
- PartialFunction
- Source
- (source)
@deprecated("Use foldLeft instead of /:", "2.13.0") @inline
- Inhertied from
- IterableOnceOps
- Source
- (source)
Finds the first element of the collection for which the given partial
function is defined, and applies the partial function to it.
Note: may not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Value Params
- pf
-
the partial function
- Returns
-
an option value containing pf applied to the first value for which it is defined, or
None
if none exists. - Example
Seq("a", 1, 5L).collectFirst({ case x: Int => x*10 }) = Some(10)
- Inhertied from
- IterableOnceOps
- Source
- (source)
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 Params
- B
-
the type of values returned by the transformation function
- K
-
the type of keys returned by the discriminator function
- Value Params
- f
-
the element transformation function
- key
-
the discriminator function
- Inhertied from
- IterableOps
- Source
- (source)
@deprecated("Use `concat` instead", "2.13.0") @inline
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
.
@deprecated("Use .to(LazyList) instead of .toStream", "2.13.0") @inline
- Inhertied from
- IterableOnceOps
- Source
- (source)
Sums up the elements of this collection.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
the result type of the
+
operator.
- Value Params
- num
-
an implicit parameter defining a set of numeric operations which includes the
+
operator to be used in forming the sum.
- Returns
-
the sum of all elements of this collection with respect to the
+
operator innum
. - Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecatedOverriding("Override indexOfSlice(that, from) instead - indexOfSlice(that) calls indexOfSlice(that, 0)", "2.13.0")
Finds first 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.
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 Params
- B
-
the type of the elements of
that
- Value Params
- p
-
the test predicate, which relates elements from both collections
- that
-
the other collection
- Returns
-
true
if both collections have the same length andp(x, y)
istrue
for all corresponding elementsx
of this iterator andy
ofthat
, otherwisefalse
- Inhertied from
- IterableOnceOps
- Source
- (source)
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 Params
- B
-
the type of the elements in the resulting collection
- Value Params
- op
-
the binary operator applied to the intermediate result and the element
- z
-
the initial value
- Returns
-
collection with intermediate results
- Inhertied from
- IterableOps
- Source
- (source)
def scala$collection$immutable$StrictOptimizedSeqOps$$super$sorted[B >: A](ord: Ordering[B]): List[A]
- Inhertied from
- StrictOptimizedSeqOps
- Source
- (source)
Folds the elements of this collection using the specified associative binary operator.
The default implementation in
IterableOnce
is equivalent to foldLeft
but may be
overridden for more efficient traversal orders. The order in which operations are performed on elements is unspecified
and may be nondeterministic.
Note: will not terminate for infinite-sized collections.
- Type Params
- A1
-
a type parameter for the binary operator, a supertype of
A
.
- Value Params
- op
-
a binary operator that must be associative.
- z
-
a neutral element for the fold operation; may be added to the result an arbitrary number of times, and must not change the result (e.g.,
Nil
for list concatenation, 0 for addition, or 1 for multiplication).
- Returns
-
the result of applying the fold operator
op
between all the elements andz
, orz
if this collection is empty. - Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecated("Iterable.seq always returns the iterable itself", "2.13.0")
Finds the first element which yields the smallest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The result type of the function f.
- Value Params
- cmp
-
An ordering to be used for comparing elements.
- f
-
The measuring function.
- 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
. - Inhertied from
- IterableOnceOps
- Source
- (source)
Convert collection to array.
Implementation note: DO NOT call Array.from from this method.
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecatedOverriding("Override indexWhere(p, from) instead - indexWhere(p) calls indexWhere(p, 0)", "2.13.0")
Finds index of the first element satisfying some predicate.
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.
- 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)
- Inhertied from
- IterableOps
- Source
- (source)
Tries to extract a
B
from an A
in a pattern matching expression.- Inhertied from
- PartialFunction
- Source
- (source)
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.
- Value Params
- size
-
the number of elements per group
- step
-
the distance between the first elements of successive groups
- Returns
-
An iterator producing iterable collections of size
size
, except the last element (which may be the only element) will be smaller if there are fewer thansize
elements remaining to be grouped. - See also
- scala.collection.Iterator, method
sliding
- Example
List(1, 2, 3, 4, 5).sliding(2, 2) = Iterator(List(1, 2), List(3, 4), List(5))
List(1, 2, 3, 4, 5, 6).sliding(2, 3) = Iterator(List(1, 2), List(4, 5))
- Inhertied from
- IterableOps
- Source
- (source)
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 Params
- size
-
the number of elements per group
- Returns
-
An iterator producing iterable collections of size
size
, except for a non-empty collection with less thansize
elements, which returns an iterator that produces the source collection itself as its only element. - See also
- 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))
- Inhertied from
- IterableOps
- Source
- (source)
@deprecated("`aggregate` is not relevant for sequential collections. Use `foldLeft(z)(seqop)` instead.", "2.13.0")
- Inhertied from
- IterableOnceOps
- Source
- (source)
Transposes this iterable collection of iterable collections into
a iterable collection of iterable collections.
The resulting collection's type will be guided by the
static type of iterable collection. 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.
- Type Params
- B
-
the type of the elements of each iterable collection.
- Value Params
- asIterable
-
an implicit conversion which asserts that the element type of this iterable collection is an
Iterable
.
- Returns
-
a two-dimensional iterable collection of iterable collections which has as nth row the nth column of this iterable collection.
- Throws
- IllegalArgumentException
- IllegalArgumentException
- Inhertied from
- IterableOps
- Source
- (source)
Creates a non-strict filter of this iterable collection.
Note: the difference between
c filter p
and c withFilter p
is that
the former creates a new collection, whereas the latter only
restricts the domain of subsequent map
, flatMap
, foreach
,
and withFilter
operations. Note: might return different results for different runs, unless the underlying collection type is ordered.
- Value Params
- p
-
the predicate used to test elements.
- Returns
-
an object of class
WithFilter
, which supportsmap
,flatMap
,foreach
, andwithFilter
operations. All these operations apply to those elements of this iterable collection which satisfy the predicatep
. - Inhertied from
- IterableOps
- Source
- (source)
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 =
scala> val h = a.addString(b)
h: StringBuilder = 1234
- Value Params
- b
-
the string builder to which elements are appended.
- Returns
-
the string builder
b
to which elements were appended. - Inhertied from
- IterableOnceOps
- Source
- (source)
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 =
scala> a.addString(b, ", ")
res0: StringBuilder = 1, 2, 3, 4
- Value Params
- b
-
the string builder to which elements are appended.
- sep
-
the separator string.
- Returns
-
the string builder
b
to which elements were appended. - Inhertied from
- IterableOnceOps
- Source
- (source)
Appends all elements of this collection 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 collection are 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 =
scala> a.addString(b , "List(" , ", " , ")")
res5: StringBuilder = List(1, 2, 3, 4)
- Value Params
- b
-
the string builder to which elements are appended.
- end
-
the ending string.
- sep
-
the separator string.
- start
-
the starting string.
- Returns
-
the string builder
b
to which elements were appended. - Inhertied from
- IterableOnceOps
- Source
- (source)
Turns this partial function into a plain function returning an
Option
result.- Returns
-
a function that takes an argument
x
toSome(this(x))
ifthis
is defined forx
, and toNone
otherwise. - See also
- Function.unlift
- Inhertied from
- PartialFunction
- Source
- (source)
@deprecated("Use toIterable instead", "2.13.0")
Converts this iterable collection to an unspecified Iterable. Will return
the same collection if this instance is already Iterable.
- Returns
-
An Iterable containing all elements of this iterable collection.
- Inhertied from
- IterableOps
- Source
- (source)
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 (as determined by
lt
) appear in the same order in the sorted sequence as in the original.
- Value Params
- lt
-
the comparison function which tests whether its first argument precedes its second argument in the desired ordering.
- Returns
-
a sequence consisting of the elements of this sequence sorted according to the comparison function
lt
. - Example
List("Steve", "Tom", "John", "Bob").sortWith(_.compareTo(_) < 0) = List("Bob", "John", "Steve", "Tom")
- Inhertied from
- SeqOps
- Source
- (source)
Finds the first element which yields the smallest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The result type of the function f.
- Value Params
- cmp
-
An ordering to be used for comparing elements.
- f
-
The measuring function.
- Returns
-
the first element of this collection with the smallest value measured by function f with respect to the ordering
cmp
. - Throws
- UnsupportedOperationException
- UnsupportedOperationException
- Inhertied from
- IterableOnceOps
- Source
- (source)
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.
@deprecatedOverriding("nonEmpty is defined as !isEmpty; override isEmpty instead", "2.13.0")
Tests whether the collection is not empty.
- Returns
-
true
if the collection contains at least one element,false
otherwise. - Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecatedOverriding("Override lastIndexWhere(p, end) instead - lastIndexWhere(p) calls lastIndexWhere(p, Int.MaxValue)", "2.13.0")
Finds index of last element satisfying some predicate.
@deprecated("Check .knownSize instead of .hasDefiniteSize for more actionable information (see scaladoc for details)", "2.13.0")
Tests whether this collection 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.
- Returns
-
true
if this collection is known to have finite size,false
otherwise. - See also
- method
knownSize
for a more useful alternative - Inhertied from
- IterableOnceOps
- Source
- (source)
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. It is highly recommended to call applyOrElse
instead of isDefinedAt / apply for efficiency.
- Type Params
- R
-
the parameter type of the transformation function.
- Value Params
- k
-
the transformation function
- Returns
-
a partial function with the domain of other partial function narrowed by this partial function, which maps arguments
x
tothis(k(x))
. - Inhertied from
- PartialFunction
- Source
- (source)
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)
- Type Params
- B
-
the type of the second element in each eventual pair
- Value Params
- that
-
the iterable providing the second element of each eventual pair
- Returns
-
a decorator
LazyZip2
that allows strict operations to be performed on the lazily evaluated pairs or chained calls tolazyZip
. Implicit conversion toIterable[(A, B)]
is also supported. - Inhertied from
- Iterable
- Source
- (source)
Applies a binary operator to all elements of this collection, going right to left.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the
underlying collection type is ordered or the operator is associative
and commutative.
- Type Params
- B
-
the result type of the binary operator.
- Value Params
- op
-
the binary operator.
- Returns
-
the result of inserting
op
between consecutive elements of this collection, going right to left:op(x1, op(x2, ..., op(xn-1, xn)...))
wherex1, ..., xn
are the elements of this collection. - Throws
- UnsupportedOperationException
- UnsupportedOperationException
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecated("Use .reverseIterator.map(f).to(...) instead of .reverseMap(f)", "2.13.0")
Finds the smallest element.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The type over which the ordering is defined.
- Value Params
- ord
-
An ordering to be used for comparing elements.
- Returns
-
the smallest element of this collection with respect to the ordering
ord
. - Throws
- UnsupportedOperationException
- UnsupportedOperationException
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecated("Use `dest ++= coll` instead", "2.13.0") @inline
- Inhertied from
- IterableOnceOps
- Source
- (source)
- Returns
-
The number of elements in this collection, if it can be cheaply computed, -1 otherwise. Cheaply usually means: Not requiring a collection traversal.
- Inhertied from
- IterableOnce
- Source
- (source)
Finds the first element which yields the largest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The result type of the function f.
- Value Params
- cmp
-
An ordering to be used for comparing elements.
- f
-
The measuring function.
- 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
. - Inhertied from
- IterableOnceOps
- Source
- (source)
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 Params
- K
-
the type of keys returned by the discriminator function.
- Value Params
- f
-
the discriminator function.
- 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 keyk
is bound to a iterable collection of those elementsx
for whichf(x)
equalsk
. - Inhertied from
- IterableOps
- Source
- (source)
@deprecated("Use .iterator instead of .toIterator", "2.13.0") @inline
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecated("Use iterableFactory instead", "2.13.0") @deprecatedOverriding("Use iterableFactory instead", "2.13.0") @inline
- Inhertied from
- IterableOps
- Source
- (source)
Finds the first element which yields the largest value measured by function f.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The result type of the function f.
- Value Params
- cmp
-
An ordering to be used for comparing elements.
- f
-
The measuring function.
- Returns
-
the first element of this collection with the largest value measured by function f with respect to the ordering
cmp
. - Throws
- UnsupportedOperationException
- UnsupportedOperationException
- Inhertied from
- IterableOnceOps
- Source
- (source)
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. It is highly recommended to call applyOrElse
instead of isDefinedAt / apply for efficiency.
- Type Params
- C
-
the result type of the transformation function.
- Value Params
- k
-
the transformation function
- Returns
-
a partial function with the domain of this partial function narrowed by other partial function, which maps arguments
x
tok(this(x))
. - Inhertied from
- PartialFunction
- Source
- (source)
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 Params
- C
-
the result type of the transformation function.
- Value Params
- k
-
the transformation function
- Returns
-
a partial function with the domain of this partial function, possibly narrowed by the specified function, which maps arguments
x
tok(this(x))
. - Definition Classes
- Inhertied from
- PartialFunction
- Source
- (source)
Partitions elements in fixed size iterable collections.
- Value Params
- size
-
the number of elements per group
- Returns
-
An iterator producing iterable collections of size
size
, except the last will be less than sizesize
if the elements don't divide evenly. - See also
- scala.collection.Iterator, method
grouped
- Inhertied from
- IterableOps
- Source
- (source)
Finds the largest element.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The type over which the ordering is defined.
- Value Params
- ord
-
An ordering to be used for comparing elements.
- Returns
-
an option value containing the largest element of this collection with respect to the ordering
ord
. - Inhertied from
- IterableOnceOps
- Source
- (source)
Multiplies up the elements of this collection.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
the result type of the
*
operator.
- Value Params
- num
-
an implicit parameter defining a set of numeric operations which includes the
*
operator to be used in forming the product.
- Returns
-
the product of all elements of this collection with respect to the
*
operator innum
. - Inhertied from
- IterableOnceOps
- Source
- (source)
Composes this partial function with a fallback partial function which
gets applied where this partial function is not defined.
- Type Params
- A1
-
the argument type of the fallback function
- B1
-
the result type of the fallback function
- Value Params
- that
-
the fallback function
- Returns
-
a partial function which has as domain the union of the domains of this partial function and
that
. The resulting partial function takesx
tothis(x)
wherethis
is defined, and tothat(x)
where it is not. - Inhertied from
- PartialFunction
- Source
- (source)
Given a collection factory
factory
, convert 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]
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecated("Use foldRight instead of :\\", "2.13.0") @inline
- Inhertied from
- IterableOnceOps
- Source
- (source)
@throws(scala.throws.$lessinit$greater$default$1[scala.IndexOutOfBoundsException])
- Definition Classes
- Inhertied from
- LinearSeqOps
- Source
- (source)
Computes a prefix scan of the elements of the collection.
Note: The neutral element
z
may be applied more than once.
- Type Params
- B
-
element type of the resulting collection
- Value Params
- op
-
the associative operator for the scan
- z
-
neutral element for the operator
op
- Returns
-
a new iterable collection containing the prefix scan of the elements in this iterable collection
- Inhertied from
- IterableOps
- Source
- (source)
Alias for
concat
- Inhertied from
- IterableOps
- Source
- (source)
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 Params
- B
-
the type of the elements of the array.
- Value Params
- len
-
the maximal number of elements to copy.
- start
-
the starting index of xs.
- xs
-
the array to fill.
- 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.
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecatedOverriding("This should always forward to the 3-arg version of this method", since = "2.13.4")
Copy 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 Params
- B
-
the type of the elements of the array.
- Value Params
- start
-
the starting index of xs.
- xs
-
the array to fill.
- 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.
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecatedOverriding("This should always forward to the 3-arg version of this method", since = "2.13.4")
Copy 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 Params
- B
-
the type of the elements of the array.
- Value Params
- xs
-
the array to fill.
- 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.
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecatedOverriding("Override lastIndexOfSlice(that, end) instead - lastIndexOfSlice(that) calls lastIndexOfSlice(that, Int.MaxValue)", "2.13.0")
Finds last 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.
Finds the smallest element.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The type over which the ordering is defined.
- Value Params
- ord
-
An ordering to be used for comparing elements.
- Returns
-
an option value containing the smallest element of this collection with respect to the ordering
ord
. - Inhertied from
- IterableOnceOps
- Source
- (source)
Search 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 Params
- 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.
- Returns
-
a
Found
value containing the index corresponding to the element in the sequence, or theInsertionPoint
where the element would be inserted if the element is not in the sequence. - See also
- Note
- if
to <= from
, the search space is empty, and anInsertionPoint
atfrom
is returned - Inhertied from
- SeqOps
- Source
- (source)
Search 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 Params
- elem
-
the element to find.
- ord
-
the ordering to be used to compare elements.
- Returns
-
a
Found
value containing the index corresponding to the element in the sequence, or theInsertionPoint
where the element would be inserted if the element is not in the sequence. - See also
- Inhertied from
- SeqOps
- Source
- (source)
Displays all elements of this collection in a string.
Delegates to addString, which can be overridden.
- 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. - Inhertied from
- IterableOnceOps
- Source
- (source)
Displays all elements of this collection in a string using a separator string.
Delegates to addString, which can be overridden.
- Value Params
- sep
-
the separator string.
- 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 stringsep
. - Example
List(1, 2, 3).mkString("|") = "1|2|3"
- Inhertied from
- IterableOnceOps
- Source
- (source)
Displays all elements of this collection in a string using start, end, and
separator strings.
Delegates to addString, which can be overridden.
- Value Params
- end
-
the ending string.
- sep
-
the separator string.
- start
-
the starting string.
- Returns
-
a string representation of this collection. The resulting string begins with the string
start
and ends with the stringend
. Inside, the string representations (w.r.t. the methodtoString
) of all elements of this collection are separated by the stringsep
. - Example
List(1, 2, 3).mkString("(", "; ", ")") = "(1; 2; 3)"
- Inhertied from
- IterableOnceOps
- Source
- (source)
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.
-
For collections of
Long
a scala.collection.LongStepper is returned -
For any other element type, an scala.collection.AnyStepper is returned
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.
- Inhertied from
- IterableOnce
- Source
- (source)
Selects the first element of this iterable collection.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Returns
-
the first element of this iterable collection.
- Throws
- NoSuchElementException
- NoSuchElementException
- Inhertied from
- IterableOps
- Source
- (source)
Reduces the elements of this collection, if any, using the specified
associative binary operator.
The order in which operations are performed on elements is unspecified
and may be nondeterministic.
- Type Params
- B
-
A type parameter for the binary operator, a supertype of
A
.
- Value Params
- op
-
A binary operator that must be associative.
- Returns
-
An option value containing result of applying reduce operator
op
between all the elements if the collection is nonempty, andNone
otherwise. - Inhertied from
- IterableOnceOps
- Source
- (source)
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.
- Inhertied from
- IterableOps
- Source
- (source)
Counts the number of elements in the collection which satisfy a predicate.
Note: will not terminate for infinite-sized collections.
- Value Params
- p
-
the predicate used to test elements.
- Returns
-
the number of elements satisfying the predicate
p
. - Inhertied from
- IterableOnceOps
- Source
- (source)
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
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.
- Inhertied from
- IterableOps
- Source
- (source)
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
- Inhertied from
- IterableOps
- Source
- (source)
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 Params
- B
-
the target type of the transformation
f
, and the type where the orderingord
is defined.
- Value Params
- f
-
the transformation function mapping elements to some other domain
B
. - ord
-
the ordering assumed on domain
B
.
- Returns
-
a sequence consisting of the elements of this sequence sorted according to the ordering where
x < y
iford.lt(f(x), f(y))
. - See also
- 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]] words.sortBy(x => (x.length, x.head)) res0: Array[String] = Array(The, dog, fox, the, lazy, over, brown, quick, jumped)
- Inhertied from
- SeqOps
- Source
- (source)
@deprecated("Use segmentLength instead of prefixLength", "2.13.0") @inline
Returns the length of the longest prefix whose elements all satisfy some predicate.
Applies a binary operator to all elements of this collection,
going left to right.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the
underlying collection type is ordered or the operator is associative
and commutative.
- Type Params
- B
-
the result type of the binary operator.
- Value Params
- op
-
the binary operator.
- Returns
-
the result of inserting
op
between consecutive elements of this collection, going left to right:op( op( ... op(x1, x2) ..., xn-1), xn)
wherex1, ..., xn
are the elements of this collection. - Throws
- UnsupportedOperationException
- UnsupportedOperationException
- Inhertied from
- IterableOnceOps
- Source
- (source)
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.
@deprecated("Use coll instead of repr in a collection implementation, use the collection value itself from the outside", "2.13.0")
- Inhertied from
- IterableOps
- Source
- (source)
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 toif(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 actionsFor 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 Params
- default
-
the fallback function
- x
-
the function argument
- Returns
-
the result of this function or fallback function application.
- Inhertied from
- PartialFunction
- Source
- (source)
@deprecatedOverriding("Override indexOf(elem, from) instead - indexOf(elem) calls indexOf(elem, 0)", "2.13.0")
Finds index of first occurrence of some value in this sequence.
The rest of the collection without its
n
last elements. For
linear, immutable collections this should avoid making a copy. Note: Even when applied to a view or a lazy collection it will always force the elements.
- Definition Classes
- Inhertied from
- StrictOptimizedIterableOps
- Source
- (source)
Returns a iterable collection formed from this iterable collection 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.
- Value Params
- that
-
the iterable providing the second half of each result pair
- thatElem
-
the element to be used to fill up the result if
that
is shorter than this iterable collection. - thisElem
-
the element to be used to fill up the result if this iterable collection is shorter than
that
.
- Returns
-
a new collection of type
That
containing pairs consisting of corresponding elements of this iterable collection andthat
. The length of the returned collection is the maximum of the lengths of this iterable collection andthat
. If this iterable collection is shorter thanthat
,thisElem
values are used to pad the result. Ifthat
is shorter than this iterable collection,thatElem
values are used to pad the result. - Inhertied from
- IterableOps
- Source
- (source)
Returns an extractor object with a
unapplySeq
method, which extracts each element of a sequence data.
- 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 }
- Inhertied from
- PartialFunction
- Source
- (source)
Iterates over combinations. A _combination_ of length
n
is a subsequence of
the original sequence, with the elements taken in order. Thus, "xy"
and "yy"
are both length-2 combinations of "xyy"
, but "yx"
is not. If there is
more than one way to generate the same subsequence, only one will be returned.For example,
"xyyy"
has three different ways to generate "xy"
depending on
whether the first, second, or third "y"
is selected. However, since all are
identical, only one will be chosen. Which of the three will be taken is an
implementation detail that is not defined. Note: Even when applied to a view or a lazy collection it will always force the elements.
Finds the largest element.
Note: will not terminate for infinite-sized collections.
- Type Params
- B
-
The type over which the ordering is defined.
- Value Params
- ord
-
An ordering to be used for comparing elements.
- Returns
-
the largest element of this collection with respect to the ordering
ord
. - Throws
- UnsupportedOperationException
- UnsupportedOperationException
- Inhertied from
- IterableOnceOps
- Source
- (source)
@deprecated("Use .view.slice(from, until) instead of .view(from, until)", "2.13.0")
A view over a slice of the elements of this collection.
- Inhertied from
- IterableOps
- Source
- (source)
Optionally applies a binary operator to all elements of this collection, going left to right.
Note: will not terminate for infinite-sized collections.
Note: might return different results for different runs, unless the
underlying collection type is ordered or the operator is associative
and commutative.
- Type Params
- B
-
the result type of the binary operator.
- Value Params
- op
-
the binary operator.
- Returns
-
an option value containing the result of
reduceLeft(op)
if this collection is nonempty,None
otherwise. - Inhertied from
- IterableOnceOps
- Source
- (source)
Reduces the elements of this collection using the specified associative binary operator.
The order in which operations are performed on elements is unspecified
and may be nondeterministic.
- Type Params
- B
-
A type parameter for the binary operator, a supertype of
A
.
- Value Params
- op
-
A binary operator that must be associative.
- Returns
-
The result of applying reduce operator
op
between all the elements if the collection is nonempty. - Throws
- UnsupportedOperationException
- UnsupportedOperationException
- Inhertied from
- IterableOnceOps
- Source
- (source)
Optionally selects the last element.
Note: might return different results for different runs, unless the underlying collection type is ordered.
- Returns
-
the last element of this iterable collection$ if it is nonempty,
None
if it is empty. - Inhertied from
- IterableOps
- Source
- (source)