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:
- List.scala

## Value members

### Concrete methods

Adds an element at the beginning of this list.

Adds an element at the beginning of this list.

- Value parameters:
- 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:
- List.scala

Adds the elements of a given list in front of this list.

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 parameters:
- prefix
The list elements to prepend.

- Returns:
a list resulting from the concatenation of the given list

`prefix`

and this list.- Source:
- List.scala

- Definition Classes
- Source:
- List.scala

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

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 parameters:
- B
the element type of the returned collection.

- Value parameters:
- 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:
- List.scala

Adds the elements of a given list in reverse order in front of this list.

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 parameters:
- prefix
the prefix to reverse and then prepend

- Returns:
the concatenation of the reversed prefix and the current list.

- Source:
- List.scala

- 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:
- List.scala

- Definition Classes
- Source:
- List.scala

- Definition Classes
- Source:
- List.scala

### Inherited methods

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 parameters:
- 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 parameters:
- 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 parameters:
- 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 parameters:
- C
the result type of the transformation function.

- Value parameters:
- 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 parameters:
- C
the result type of the transformation function.

- Value parameters:
- 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

- Definition Classes
- Inherited from:
- LinearSeqOps
- Source:
- LinearSeq.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 parameters:
- 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 parameters:
- 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 parameters:
- R
the parameter type of the transformation function.

- Value parameters:
- 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 parameters:
- A
the type to which function

`g`

can be applied

- Value parameters:
- 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 parameters:
- B
the type of the elements of the array.

- Value parameters:
- len
the maximal number of elements to copy.

- start
the starting index of xs.

- xs
the array to fill.

- 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 parameters:
- B
the type of the elements of the array.

- Value parameters:
- 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 parameters:
- B
the type of the elements of the array.

- Value parameters:
- 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 parameters:
- B
the type of the elements of

`that`

- Value parameters:
- p
the test predicate, which relates elements from both collections

- that
the other collection

- 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

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

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

Note: will not terminate for infinite-sized collections.

- Value parameters:
- p
the predicate used to test elements.

- 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 parameters:
- A1
a type parameter for the binary operator, a supertype of

`A`

.

- Value parameters:
- 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

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

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

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

- Type parameters:
- K
the type of keys returned by the discriminator function.

- Value parameters:
- f
the discriminator function.

- 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 parameters:
- B
the type of values returned by the transformation function

- K
the type of keys returned by the discriminator function

- Value parameters:
- f
the element transformation function

- key
the discriminator function

- 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 parameters:
- 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

Selects the first element of this iterable collection.

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
if the iterable collection is empty.

- 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 parameters:
- B
the type of the second element in each eventual pair

- Value parameters:
- 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 parameters:
- B
The type over which the ordering is defined.

- Value parameters:
- 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 parameters:
- B
The result type of the function f.

- Value parameters:
- 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 parameters:
- B
The result type of the function f.

- Value parameters:
- 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 parameters:
- B
The type over which the ordering is defined.

- Value parameters:
- 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 parameters:
- B
The type over which the ordering is defined.

- Value parameters:
- 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 parameters:
- B
The result type of the function f.

- Value parameters:
- 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 parameters:
- B
The result type of the function f.

- Value parameters:
- 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 parameters:
- B
The type over which the ordering is defined.

- Value parameters:
- 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 parameters:
- 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 parameters:
- 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 parameters:
- A1
the argument type of the fallback function

- B1
the result type of the fallback function

- Value parameters:
- 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 parameters:
- B
the result type of the

`*`

operator.

- Value parameters:
- num
an implicit parameter defining a set of numeric operations which includes the

`*`

operator to be used in forming the product.

- 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 parameters:
- B
A type parameter for the binary operator, a supertype of

`A`

.

- Value parameters:
- 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 parameters:
- B
the result type of the binary operator.

- Value parameters:
- 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 parameters:
- B
the result type of the binary operator.

- Value parameters:
- 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 parameters:
- B
A type parameter for the binary operator, a supertype of

`A`

.

- Value parameters:
- 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.

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

- Type parameters:
- B
the result type of the binary operator.

- Value parameters:
- 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 parameters:
- B
the result type of the binary operator.

- Value parameters:
- 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

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 parameters:
- 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 parameters:
- B
element type of the resulting collection

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

Example:

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

- Type parameters:
- B
the type of the elements in the resulting collection

- Value parameters:
- op
the binary operator applied to the intermediate result and the element

- z
the initial value

- 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 parameters:
- elem
the element to find.

- from
the index where the search starts.

- ord
the ordering to be used to compare elements.

- to
the index following where the search ends.

- 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 parameters:
- 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 parameters:
- 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 parameters:
- 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 parameters:
- B
the target type of the transformation

`f`

, and the type where the ordering`ord`

is defined.

- Value parameters:
- f
the transformation function mapping elements to some other domain

`B`

.- ord
the ordering assumed on domain

`B`

.

- 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 parameters:
- 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 parameters:
- B
the result type of the

`+`

operator.

- Value parameters:
- num
an implicit parameter defining a set of numeric operations which includes the

`+`

operator to be used in forming the sum.

- Returns:
the sum of all elements of this collection with respect to the

`+`

operator in`num`

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

The rest of the collection without its first element.

The rest of the collection without its first element.

- 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

- 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 parameters:
- B
the type of the elements of each iterable collection.

- Value parameters:
- 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

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 parameters:
- 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 parameters:
- 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