`Queue`

objects implement data structures that allow to
insert and retrieve elements in a first-in-first-out (FIFO) manner.

`Queue`

is implemented as a pair of `List`

s, one containing the in elements and the other the out elements.
Elements are added to the in list and removed from the out list. When the out list runs dry, the
queue is pivoted by replacing the out list by in.reverse, and in by Nil.

Adding items to the queue always has cost `O(1)`

. Removing items has cost `O(1)`

, except in the case
where a pivot is required, in which case, a cost of `O(n)`

is incurred, where `n`

is the number of elements in the queue. When this happens,
`n`

remove operations with `O(1)`

cost are guaranteed. Removing an item is on average `O(1)`

.

- See also
"Scala's Collection Library overview" section on

`Immutable Queues`

for more information.- Companion
- object
- Source
- Queue.scala

## Value members

### Concrete methods

Returns the `n`

-th element of this queue.

Returns the `n`

-th element of this queue.
The first element is at position `0`

.

- Value Params
- n
index of the element to return

- Returns
the element at position

`n`

in this queue.- Throws
- NoSuchElementException
if the queue is too short.

- Definition Classes
- Source
- Queue.scala

Returns a tuple with the first element in the queue, and a new queue with this element removed.

Returns a tuple with the first element in the queue, and a new queue with this element removed.

- Returns
the first element of the queue.

- Source
- Queue.scala

Optionally retrieves the first element and a queue of the remaining elements.

Optionally retrieves the first element and a queue of the remaining elements.

- Returns
A tuple of the first element of the queue, and a new queue with this element removed. If the queue is empty,

`None`

is returned.- Source
- Queue.scala

Creates a new queue with element added at the end of the old queue.

Creates a new queue with element added at the end of the old queue.

- Value Params
- elem
the element to insert

- Source
- Queue.scala

Creates a new queue with all elements provided by an `Iterable`

object
added at the end of the old queue.

Creates a new queue with all elements provided by an `Iterable`

object
added at the end of the old queue.

The elements are appended in the order they are given out by the iterator.

- Value Params
- iter
an iterable object

- Source
- Queue.scala

Returns the first element in the queue, or throws an error if there is no element contained in the queue.

Returns the first element in the queue, or throws an error if there is no element contained in the queue.

- Returns
the first element.

- Source
- Queue.scala

Checks if the queue is empty.

Checks if the queue is empty.

- Returns
true, iff there is no element in the queue.

- Definition Classes
- Source
- Queue.scala

Returns the elements in the list as an iterator

Returns the elements in the list as an iterator

- Definition Classes
- Source
- Queue.scala

### Deprecated methods

Creates a new queue with all elements provided by an `Iterable`

object
added at the end of the old queue.

`Iterable`

object
added at the end of the old queue.

The elements are appended in the order they are given out by the iterator.

- Value Params
- iter
an iterable object

- Deprecated
- Source
- Queue.scala

### Inherited methods

Alias for `concat`

Alias for `concat`

- Inherited from
- IterableOps
- Source
- Iterable.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 =
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.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 =
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.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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

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.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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. 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`

to`k(this(x))`

.- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

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 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`

to`k(this(x))`

.- Definition Classes
- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

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 Params
- default
the fallback function

- x
the function argument

- Returns
the result of this function or fallback function application.

- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

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

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)`

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Iterates over combinations.

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.

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. 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`

to`this(k(x))`

.- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

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 Params
- A
the type to which function

`g`

can be applied

- Value Params
- g
a function A => T1

- Returns
a new function

`f`

such that`f(x) == apply(g(x))`

- Inherited from
- Function1
- Source
- Function1.scala

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 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.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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 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

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 Params
- B
the type of the elements of

`that`

- Value Params
- p
the test predicate, which relates elements from both sequences

- that
the other sequence

- 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

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 Params
- p
the predicate used to test elements.

- Returns
the number of elements satisfying the predicate

`p`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

The rest of the collection without its `n`

last elements.

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
- Inherited from
- StrictOptimizedIterableOps
- Source
- StrictOptimizedIterableOps.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.

- 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

Folds the elements of this collection using the specified associative binary operator.

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 and`z`

, or`z`

if this collection is empty.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Applies a binary operator to all elements of this collection and a start value, going right to left.

Applies a binary operator to all elements of this collection and a start value, 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.

- z
the start value.

- Returns
the result of inserting

`op`

between consecutive elements of this collection, going right to left with the start value`z`

on the right:`op(x1, op(x2, ... op(xn, z)...))`

where`x1, ..., xn`

are the elements of this collection. Returns`z`

if this collection is empty.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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 key

`k`

is bound to a iterable collection of those elements`x`

for which`f(x)`

equals`k`

.- Inherited from
- IterableOps
- Source
- Iterable.scala

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 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

- Inherited from
- IterableOps
- Source
- Iterable.scala

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.

- Inherited from
- IterableOps
- Source
- Iterable.scala

Partitions elements in fixed size iterable collections.

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 size`size`

if the elements don't divide evenly.- See also
scala.collection.Iterator, method

`grouped`

- Inherited from
- IterableOps
- Source
- Iterable.scala

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

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

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.

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.

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.

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.

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.

- 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.

- 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

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

- Inherited from
- IterableOnce
- Source
- IterableOnce.scala

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.

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.

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.

Finds index of last element satisfying some predicate.

Finds index of last element satisfying some predicate.

Note: will not terminate for infinite-sized collections.

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.

- Returns
the last element of this iterable collection$ if it is nonempty,

`None`

if it is empty.- Inherited from
- IterableOps
- Source
- Iterable.scala

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)
```

- 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 to`lazyZip`

. Implicit conversion to`Iterable[(A, B)]`

is also supported.- Inherited from
- Iterable
- Source
- Iterable.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
```

Turns this partial function into a plain function returning an `Option`

result.

Turns this partial function into a plain function returning an `Option`

result.

- Returns
a function that takes an argument

`x`

to`Some(this(x))`

if`this`

is defined for`x`

, and to`None`

otherwise.- See also
Function.unlift

- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

Finds the largest element.

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
if this collection is empty.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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
if this collection is empty.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Finds the largest element.

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`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Finds the smallest element.

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
if this collection is empty.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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
if this collection is empty.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Finds the smallest element.

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`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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.

- 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

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 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 string`sep`

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

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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 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

Tests whether the collection is not empty.

Tests whether the collection is not empty.

- Returns
`true`

if the collection contains at least one element,`false`

otherwise.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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 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 takes`x`

to`this(x)`

where`this`

is defined, and to`that(x)`

where it is not.- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

Multiplies up the elements of this collection.

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 in`num`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Reduces the elements of this collection using the specified associative binary operator.

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
if this collection is empty.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Applies a binary operator to all elements of this collection, going left to right.

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)`

where`x1, ..., xn`

are the elements of this collection.- Throws
- UnsupportedOperationException
if this collection is empty.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Optionally applies a binary operator to all elements of this collection, going left to right.

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.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Reduces the elements of this collection, if any, using the specified associative binary operator.

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, and`None`

otherwise.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Applies a binary operator to all elements of this collection, going right to left.

Applies a binary operator to all elements of this collection, going right to left.

Note: will not terminate for infinite-sized collections.

- 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)...))`

where`x1, ..., xn`

are the elements of this collection.- Throws
- UnsupportedOperationException
if this collection is empty.

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Optionally applies a binary operator to all elements of this collection, going right to left.

Optionally applies a binary operator to all elements of this collection, going right to left.

Note: will not terminate for infinite-sized collections.

- 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.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Returns new sequence with elements in reversed order.

Returns new sequence with elements in reversed 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.

An iterator yielding elements in reversed order.

An iterator yielding elements in reversed order.

Note: will not terminate for infinite-sized collections.

Note: `xs.reverseIterator`

is the same as `xs.reverse.iterator`

but might be more efficient.

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 Params
- action
the action function

- Returns
a function which maps arguments

`x`

to`isDefinedAt(x)`

. The resulting function runs`action(this(x))`

where`this`

is defined.- See also
`applyOrElse`

.- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

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 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

- Inherited from
- IterableOps
- Source
- Iterable.scala

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 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

- Inherited from
- IterableOps
- Source
- Iterable.scala

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

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 the`InsertionPoint`

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 an`InsertionPoint`

at`from`

is returned- Inherited from
- SeqOps
- Source
- Seq.scala

Search this sorted sequence for a specific element.

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 the`InsertionPoint`

where the element would be inserted if the element is not in the sequence.- See also
- Inherited from
- SeqOps
- Source
- Seq.scala

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.

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
```

- Inherited from
- IterableOps
- Source
- Iterable.scala

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.

- 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 than`size`

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))`

- Inherited from
- IterableOps
- Source
- Iterable.scala

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 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 than`size`

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))`

- Inherited from
- IterableOps
- Source
- Iterable.scala

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 Params
- B
the target type of the transformation

`f`

, and the type where the ordering`ord`

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`

if`ord.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)`

- Inherited from
- SeqOps
- Source
- Seq.scala

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 (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")`

- Inherited from
- SeqOps
- Source
- Seq.scala

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.

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.

For collections of

`Int`

,`Short`

,`Byte`

or`Char`

, an scala.collection.IntStepper is returnedFor collections of

`Double`

or`Float`

, a scala.collection.DoubleStepper is returnedFor collections of

`Long`

a scala.collection.LongStepper is returnedFor 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.

- Inherited from
- IterableOnce
- Source
- IterableOnce.scala

Sums up the elements of this collection.

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 in`num`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

A collection containing the last `n`

elements of this collection.

A collection containing the last `n`

elements of this collection.

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

- Definition Classes
- Inherited from
- StrictOptimizedIterableOps
- Source
- StrictOptimizedIterableOps.scala

Takes longest prefix of elements that satisfy a predicate.

Takes longest prefix of elements that satisfy a predicate.

- Value Params
- p
The predicate used to test elements.

- Returns
the longest prefix of this iterable collection whose elements all satisfy the predicate

`p`

.- Inherited from
- IterableOps
- Source
- Iterable.scala

Given a collection factory `factory`

, convert this collection to the appropriate
representation for the current element type `A`

.

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]

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Convert collection to array.

Convert collection to array.

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

- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Transposes this iterable collection of iterable collections into a iterable collection of iterable collections.

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
if all collections in this iterable collection are not of the same size.

- Inherited from
- IterableOps
- Source
- Iterable.scala

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.

- Inherited from
- PartialFunction
- Source
- PartialFunction.scala

- Definition Classes
- Inherited from
- StrictOptimizedIterableOps
- Source
- StrictOptimizedIterableOps.scala

Creates a non-strict filter of this iterable collection.

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.

- Value Params
- p
the predicate used to test elements.

- Returns
an object of class

`WithFilter`

, which supports`map`

,`flatMap`

,`foreach`

, and`withFilter`

operations. All these operations apply to those elements of this iterable collection which satisfy the predicate`p`

.- Inherited from
- IterableOps
- Source
- Iterable.scala

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

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 and`that`

. The length of the returned collection is the maximum of the lengths of this iterable collection and`that`

. If this iterable collection is shorter than`that`

,`thisElem`

values are used to pad the result. If`that`

is shorter than this iterable collection,`thatElem`

values are used to pad the result.- Inherited from
- IterableOps
- Source
- Iterable.scala

### Deprecated and Inherited methods

- Deprecated
- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

- Deprecated
- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

- Deprecated
- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

- Deprecated
- Inherited from
- IterableOps
- Source
- Iterable.scala

- Deprecated
- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

Tests whether this collection is known to have a finite size.

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- Deprecated
This method is deprecated in 2.13 because it does not provide any actionable information. As noted above, even the collection library itself does not use it. When there is no guarantee that a collection is finite, it is generally best to attempt a computation anyway and document that it will not terminate for infinite collections rather than backing out because this would prevent performing the computation on collections that are in fact finite even though

`hasDefiniteSize`

returns`false`

.- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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.

- Deprecated
- Inherited from
- IterableOps
- Source
- Iterable.scala

- Deprecated
- Inherited from
- Iterable
- Source
- Iterable.scala

- Deprecated
- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

- Deprecated
- Inherited from
- IterableOnceOps
- Source
- IterableOnce.scala

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.

- Returns
An Iterable containing all elements of this iterable collection.

- Deprecated
- Inherited from
- IterableOps
- Source
- Iterable.scala

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`

.

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

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

- Deprecated
- Inherited from
- IterableOps
- Source
- Iterable.scala