size

abstract val size: Int

Returns the size of the collection.

contains

abstract fun contains(element: E): Boolean

Checks if the specified element is contained in this collection.

containsAll

abstract fun containsAll(elements: Collection<E>): Boolean

Checks if all elements in the specified collection are contained in this collection.

isEmpty

abstract fun isEmpty(): Boolean

Returns true if the collection is empty (contains no elements), false otherwise.

iterator

abstract fun iterator(): Iterator<E>

Returns an iterator over the elements of this object.

indices

val Collection<*>.indices: IntRange

Returns an IntRange of the valid indices for this collection.

all

fun <T> Iterable<T>.all(predicate: (T) -> Boolean): Boolean

Returns true if all elements match the given predicate.

any

fun <T> Iterable<T>.any(): Boolean

Returns true if collection has at least one element.

fun <T> Iterable<T>.any(predicate: (T) -> Boolean): Boolean

Returns true if at least one element matches the given predicate.

asIterable

fun <T> Iterable<T>.asIterable(): Iterable<T>

Returns this collection as an Iterable.

asSequence

fun <T> Iterable<T>.asSequence(): Sequence<T>

Creates a Sequence instance that wraps the original collection returning its elements when being iterated.

associate

fun <T, K, V> Iterable<T>.associate(
    transform: (T) -> Pair<K, V>
): Map<K, V>

Returns a Map containing key-value pairs provided by transform function applied to elements of the given collection.

associateBy

fun <T, K> Iterable<T>.associateBy(
    keySelector: (T) -> K
): Map<K, T>

Returns a Map containing the elements from the given collection indexed by the key returned from keySelector function applied to each element.

fun <T, K, V> Iterable<T>.associateBy(
    keySelector: (T) -> K, 
    valueTransform: (T) -> V
): Map<K, V>

Returns a Map containing the values provided by valueTransform and indexed by keySelector functions applied to elements of the given collection.

associateByTo

fun <T, K, M : MutableMap<in K, in T>> Iterable<T>.associateByTo(
    destination: M, 
    keySelector: (T) -> K
): M

Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function applied to each element of the given collection and value is the element itself.

fun <T, K, V, M : MutableMap<in K, in V>> Iterable<T>.associateByTo(
    destination: M, 
    keySelector: (T) -> K, 
    valueTransform: (T) -> V
): M

Populates and returns the destination mutable map with key-value pairs, where key is provided by the keySelector function and and value is provided by the valueTransform function applied to elements of the given collection.

associateTo

fun <T, K, V, M : MutableMap<in K, in V>> Iterable<T>.associateTo(
    destination: M, 
    transform: (T) -> Pair<K, V>
): M

Populates and returns the destination mutable map with key-value pairs provided by transform function applied to each element of the given collection.

contains

operator fun <T> Iterable<T>.contains(element: T): Boolean

Returns true if element is found in the collection.

containsAll

fun <T> Collection<T>.containsAll(
    elements: Collection<T>
): Boolean

Checks if all elements in the specified collection are contained in this collection.

count

fun <T> Iterable<T>.count(predicate: (T) -> Boolean): Int

Returns the number of elements matching the given predicate.

distinct

fun <T> Iterable<T>.distinct(): List<T>

Returns a list containing only distinct elements from the given collection.

distinctBy

fun <T, K> Iterable<T>.distinctBy(
    selector: (T) -> K
): List<T>

Returns a list containing only elements from the given collection having distinct keys returned by the given selector function.

drop

fun <T> Iterable<T>.drop(n: Int): List<T>

Returns a list containing all elements except first n elements.

dropWhile

fun <T> Iterable<T>.dropWhile(
    predicate: (T) -> Boolean
): List<T>

Returns a list containing all elements except first elements that satisfy the given predicate.

elementAt

fun <T> Iterable<T>.elementAt(index: Int): T

Returns an element at the given index or throws an IndexOutOfBoundsException if the index is out of bounds of this collection.

elementAtOrElse

fun <T> Iterable<T>.elementAtOrElse(
    index: Int, 
    defaultValue: (Int) -> T
): T

Returns an element at the given index or the result of calling the defaultValue function if the index is out of bounds of this collection.

elementAtOrNull

fun <T> Iterable<T>.elementAtOrNull(index: Int): T?

Returns an element at the given index or null if the index is out of bounds of this collection.

filter

fun <T> Iterable<T>.filter(
    predicate: (T) -> Boolean
): List<T>

Returns a list containing only elements matching the given predicate.

filterIndexed

fun <T> Iterable<T>.filterIndexed(
    predicate: (index: Int, T) -> Boolean
): List<T>

Returns a list containing only elements matching the given predicate.

filterIndexedTo

fun <T, C : MutableCollection<in T>> Iterable<T>.filterIndexedTo(
    destination: C, 
    predicate: (index: Int, T) -> Boolean
): C

Appends all elements matching the given predicate to the given destination.

filterIsInstance

fun <R> Iterable<*>.filterIsInstance(): List<R>

Returns a list containing all elements that are instances of specified type parameter R.

fun <R> Iterable<*>.filterIsInstance(
    klass: Class<R>
): List<R>

Returns a list containing all elements that are instances of specified class.

filterIsInstanceTo

fun <R, C : MutableCollection<in R>> Iterable<*>.filterIsInstanceTo(
    destination: C
): C

Appends all elements that are instances of specified type parameter R to the given destination.

fun <C : MutableCollection<in R>, R> Iterable<*>.filterIsInstanceTo(
    destination: C, 
    klass: Class<R>
): C

Appends all elements that are instances of specified class to the given destination.

filterNot

fun <T> Iterable<T>.filterNot(
    predicate: (T) -> Boolean
): List<T>

Returns a list containing all elements not matching the given predicate.

filterNotNull

fun <T : Any> Iterable<T?>.filterNotNull(): List<T>

Returns a list containing all elements that are not null.

filterNotNullTo

fun <C : MutableCollection<in T>, T : Any> Iterable<T?>.filterNotNullTo(
    destination: C
): C

Appends all elements that are not null to the given destination.

filterNotTo

fun <T, C : MutableCollection<in T>> Iterable<T>.filterNotTo(
    destination: C, 
    predicate: (T) -> Boolean
): C

Appends all elements not matching the given predicate to the given destination.

filterTo

fun <T, C : MutableCollection<in T>> Iterable<T>.filterTo(
    destination: C, 
    predicate: (T) -> Boolean
): C

Appends all elements matching the given predicate to the given destination.

find

fun <T> Iterable<T>.find(predicate: (T) -> Boolean): T?

Returns the first element matching the given predicate, or null if no such element was found.

findLast

fun <T> Iterable<T>.findLast(predicate: (T) -> Boolean): T?

Returns the last element matching the given predicate, or null if no such element was found.

first

fun <T> Iterable<T>.first(): T

Returns first element.

fun <T> Iterable<T>.first(predicate: (T) -> Boolean): T

Returns the first element matching the given predicate.

firstOrNull

fun <T> Iterable<T>.firstOrNull(): T?

Returns the first element, or null if the collection is empty.

fun <T> Iterable<T>.firstOrNull(
    predicate: (T) -> Boolean
): T?

Returns the first element matching the given predicate, or null if element was not found.

flatMap

fun <T, R> Iterable<T>.flatMap(
    transform: (T) -> Iterable<R>
): List<R>

Returns a single list of all elements yielded from results of transform function being invoked on each element of original collection.

flatMapTo

fun <T, R, C : MutableCollection<in R>> Iterable<T>.flatMapTo(
    destination: C, 
    transform: (T) -> Iterable<R>
): C

Appends all elements yielded from results of transform function being invoked on each element of original collection, to the given destination.

fold

fun <T, R> Iterable<T>.fold(
    initial: R, 
    operation: (acc: R, T) -> R
): R

Accumulates value starting with initial value and applying operation from left to right to current accumulator value and each element.

foldIndexed

fun <T, R> Iterable<T>.foldIndexed(
    initial: R, 
    operation: (index: Int, acc: R, T) -> R
): R

Accumulates value starting with initial value and applying operation from left to right to current accumulator value and each element with its index in the original collection.

forEach

fun <T> Iterable<T>.forEach(action: (T) -> Unit)

Performs the given action on each element.

forEachIndexed

fun <T> Iterable<T>.forEachIndexed(
    action: (index: Int, T) -> Unit)

Performs the given action on each element, providing sequential index with the element.

groupBy

fun <T, K> Iterable<T>.groupBy(
    keySelector: (T) -> K
): Map<K, List<T>>

Groups elements of the original collection by the key returned by the given keySelector function applied to each element and returns a map where each group key is associated with a list of corresponding elements.

fun <T, K, V> Iterable<T>.groupBy(
    keySelector: (T) -> K, 
    valueTransform: (T) -> V
): Map<K, List<V>>

Groups values returned by the valueTransform function applied to each element of the original collection by the key returned by the given keySelector function applied to the element and returns a map where each group key is associated with a list of corresponding values.

groupByTo

fun <T, K, M : MutableMap<in K, MutableList<T>>> Iterable<T>.groupByTo(
    destination: M, 
    keySelector: (T) -> K
): M

Groups elements of the original collection by the key returned by the given keySelector function applied to each element and puts to the destination map each group key associated with a list of corresponding elements.

fun <T, K, V, M : MutableMap<in K, MutableList<V>>> Iterable<T>.groupByTo(
    destination: M, 
    keySelector: (T) -> K, 
    valueTransform: (T) -> V
): M

Groups values returned by the valueTransform function applied to each element of the original collection by the key returned by the given keySelector function applied to the element and puts to the destination map each group key associated with a list of corresponding values.

groupingBy

fun <T, K> Iterable<T>.groupingBy(
    keySelector: (T) -> K
): Grouping<T, K>

Creates a Grouping source from a collection to be used later with one of group-and-fold operations using the specified keySelector function to extract a key from each element.

indexOf

fun <T> Iterable<T>.indexOf(element: T): Int

Returns first index of element, or -1 if the collection does not contain element.

indexOfFirst

fun <T> Iterable<T>.indexOfFirst(
    predicate: (T) -> Boolean
): Int

Returns index of the first element matching the given predicate, or -1 if the collection does not contain such element.

indexOfLast

fun <T> Iterable<T>.indexOfLast(
    predicate: (T) -> Boolean
): Int

Returns index of the last element matching the given predicate, or -1 if the collection does not contain such element.

intersect

infix fun <T> Iterable<T>.intersect(
    other: Iterable<T>
): Set<T>

Returns a set containing all elements that are contained by both this set and the specified collection.

isNotEmpty

fun <T> Collection<T>.isNotEmpty(): Boolean

Returns true if the collection is not empty.

joinTo

fun <T, A : Appendable> Iterable<T>.joinTo(
    buffer: A, 
    separator: CharSequence = ", ", 
    prefix: CharSequence = "", 
    postfix: CharSequence = "", 
    limit: Int = -1, 
    truncated: CharSequence = "...", 
    transform: (T) -> CharSequence = null
): A

Appends the string from all the elements separated using separator and using the given prefix and postfix if supplied.

joinToString

fun <T> Iterable<T>.joinToString(
    separator: CharSequence = ", ", 
    prefix: CharSequence = "", 
    postfix: CharSequence = "", 
    limit: Int = -1, 
    truncated: CharSequence = "...", 
    transform: (T) -> CharSequence = null
): String

Creates a string from all the elements separated using separator and using the given prefix and postfix if supplied.

last

fun <T> Iterable<T>.last(): T

Returns the last element.

fun <T> Iterable<T>.last(predicate: (T) -> Boolean): T

Returns the last element matching the given predicate.

lastIndexOf

fun <T> Iterable<T>.lastIndexOf(element: T): Int

Returns last index of element, or -1 if the collection does not contain element.

lastOrNull

fun <T> Iterable<T>.lastOrNull(): T?

Returns the last element, or null if the collection is empty.

fun <T> Iterable<T>.lastOrNull(predicate: (T) -> Boolean): T?

Returns the last element matching the given predicate, or null if no such element was found.

map

fun <T, R> Iterable<T>.map(transform: (T) -> R): List<R>

Returns a list containing the results of applying the given transform function to each element in the original collection.

mapIndexed

fun <T, R> Iterable<T>.mapIndexed(
    transform: (index: Int, T) -> R
): List<R>

Returns a list containing the results of applying the given transform function to each element and its index in the original collection.

mapIndexedNotNull

fun <T, R : Any> Iterable<T>.mapIndexedNotNull(
    transform: (index: Int, T) -> R?
): List<R>

Returns a list containing only the non-null results of applying the given transform function to each element and its index in the original collection.

mapIndexedNotNullTo

fun <T, R : Any, C : MutableCollection<in R>> Iterable<T>.mapIndexedNotNullTo(
    destination: C, 
    transform: (index: Int, T) -> R?
): C

Applies the given transform function to each element and its index in the original collection and appends only the non-null results to the given destination.

mapIndexedTo

fun <T, R, C : MutableCollection<in R>> Iterable<T>.mapIndexedTo(
    destination: C, 
    transform: (index: Int, T) -> R
): C

Applies the given transform function to each element and its index in the original collection and appends the results to the given destination.

mapNotNull

fun <T, R : Any> Iterable<T>.mapNotNull(
    transform: (T) -> R?
): List<R>

Returns a list containing only the non-null results of applying the given transform function to each element in the original collection.

mapNotNullTo

fun <T, R : Any, C : MutableCollection<in R>> Iterable<T>.mapNotNullTo(
    destination: C, 
    transform: (T) -> R?
): C

Applies the given transform function to each element in the original collection and appends only the non-null results to the given destination.

mapTo

fun <T, R, C : MutableCollection<in R>> Iterable<T>.mapTo(
    destination: C, 
    transform: (T) -> R
): C

Applies the given transform function to each element of the original collection and appends the results to the given destination.

max

fun <T : Comparable<T>> Iterable<T>.max(): T?

Returns the largest element or null if there are no elements.

maxBy

fun <T, R : Comparable<R>> Iterable<T>.maxBy(
    selector: (T) -> R
): T?

Returns the first element yielding the largest value of the given function or null if there are no elements.

maxWith

fun <T> Iterable<T>.maxWith(comparator: Comparator<in T>): T?

fun <T> Iterable<T>.maxWith(comparator: Comparator<in T>): T?

Returns the first element having the largest value according to the provided comparator or null if there are no elements.

min

fun <T : Comparable<T>> Iterable<T>.min(): T?

Returns the smallest element or null if there are no elements.

minBy

fun <T, R : Comparable<R>> Iterable<T>.minBy(
    selector: (T) -> R
): T?

Returns the first element yielding the smallest value of the given function or null if there are no elements.

minWith

fun <T> Iterable<T>.minWith(comparator: Comparator<in T>): T?

fun <T> Iterable<T>.minWith(comparator: Comparator<in T>): T?

Returns the first element having the smallest value according to the provided comparator or null if there are no elements.

minus

operator fun <T> Set<T>.minus(element: T): Set<T>

Returns a set containing all elements of the original set except the given element.

operator fun <T> Set<T>.minus(elements: Array<out T>): Set<T>

Returns a set containing all elements of the original set except the elements contained in the given elements array.

operator fun <T> Set<T>.minus(elements: Iterable<T>): Set<T>

Returns a set containing all elements of the original set except the elements contained in the given elements collection.

operator fun <T> Set<T>.minus(elements: Sequence<T>): Set<T>

Returns a set containing all elements of the original set except the elements contained in the given elements sequence.

operator fun <T> Iterable<T>.minus(element: T): List<T>

Returns a list containing all elements of the original collection without the first occurrence of the given element.

operator fun <T> Iterable<T>.minus(
    elements: Array<out T>
): List<T>

Returns a list containing all elements of the original collection except the elements contained in the given elements array.

operator fun <T> Iterable<T>.minus(
    elements: Iterable<T>
): List<T>

Returns a list containing all elements of the original collection except the elements contained in the given elements collection.

operator fun <T> Iterable<T>.minus(
    elements: Sequence<T>
): List<T>

Returns a list containing all elements of the original collection except the elements contained in the given elements sequence.

minusElement

fun <T> Set<T>.minusElement(element: T): Set<T>

Returns a set containing all elements of the original set except the given element.

fun <T> Iterable<T>.minusElement(element: T): List<T>

Returns a list containing all elements of the original collection without the first occurrence of the given element.

none

fun <T> Iterable<T>.none(): Boolean

Returns true if the collection has no elements.

fun <T> Iterable<T>.none(predicate: (T) -> Boolean): Boolean

Returns true if no elements match the given predicate.

orEmpty

fun <T> Set<T>?.orEmpty(): Set<T>

Returns this Set if it's not null and the empty set otherwise.

partition

fun <T> Iterable<T>.partition(
    predicate: (T) -> Boolean
): Pair<List<T>, List<T>>

Splits the original collection into pair of lists, where first list contains elements for which predicate yielded true, while second list contains elements for which predicate yielded false.

plus

operator fun <T> Set<T>.plus(element: T): Set<T>

Returns a set containing all elements of the original set and then the given element if it isn't already in this set.

operator fun <T> Set<T>.plus(elements: Array<out T>): Set<T>

Returns a set containing all elements of the original set and the given elements array, which aren't already in this set.

operator fun <T> Set<T>.plus(elements: Iterable<T>): Set<T>

Returns a set containing all elements of the original set and the given elements collection, which aren't already in this set. The returned set preserves the element iteration order of the original set.

operator fun <T> Set<T>.plus(elements: Sequence<T>): Set<T>

Returns a set containing all elements of the original set and the given elements sequence, which aren't already in this set.

operator fun <T> Iterable<T>.plus(element: T): List<T>

operator fun <T> Collection<T>.plus(element: T): List<T>

Returns a list containing all elements of the original collection and then the given element.

operator fun <T> Iterable<T>.plus(
    elements: Array<out T>
): List<T>

operator fun <T> Collection<T>.plus(
    elements: Array<out T>
): List<T>

Returns a list containing all elements of the original collection and then all elements of the given elements array.

operator fun <T> Iterable<T>.plus(
    elements: Iterable<T>
): List<T>

operator fun <T> Collection<T>.plus(
    elements: Iterable<T>
): List<T>

Returns a list containing all elements of the original collection and then all elements of the given elements collection.

operator fun <T> Iterable<T>.plus(
    elements: Sequence<T>
): List<T>

operator fun <T> Collection<T>.plus(
    elements: Sequence<T>
): List<T>

Returns a list containing all elements of the original collection and then all elements of the given elements sequence.

plusElement

fun <T> Set<T>.plusElement(element: T): Set<T>

Returns a set containing all elements of the original set and then the given element if it isn't already in this set.

fun <T> Iterable<T>.plusElement(element: T): List<T>

fun <T> Collection<T>.plusElement(element: T): List<T>

Returns a list containing all elements of the original collection and then the given element.

reduce

fun <S, T : S> Iterable<T>.reduce(
    operation: (acc: S, T) -> S
): S

Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element.

reduceIndexed

fun <S, T : S> Iterable<T>.reduceIndexed(
    operation: (index: Int, acc: S, T) -> S
): S

Accumulates value starting with the first element and applying operation from left to right to current accumulator value and each element with its index in the original collection.

requireNoNulls

fun <T : Any> Iterable<T?>.requireNoNulls(): Iterable<T>

Returns an original collection containing all the non-null elements, throwing an IllegalArgumentException if there are any null elements.

reversed

fun <T> Iterable<T>.reversed(): List<T>

Returns a list with elements in reversed order.

single

fun <T> Iterable<T>.single(): T

Returns the single element, or throws an exception if the collection is empty or has more than one element.

fun <T> Iterable<T>.single(predicate: (T) -> Boolean): T

Returns the single element matching the given predicate, or throws exception if there is no or more than one matching element.

singleOrNull

fun <T> Iterable<T>.singleOrNull(): T?

Returns single element, or null if the collection is empty or has more than one element.

fun <T> Iterable<T>.singleOrNull(
    predicate: (T) -> Boolean
): T?

Returns the single element matching the given predicate, or null if element was not found or more than one element was found.

sorted

fun <T : Comparable<T>> Iterable<T>.sorted(): List<T>

Returns a list of all elements sorted according to their natural sort order.

sortedBy

fun <T, R : Comparable<R>> Iterable<T>.sortedBy(
    selector: (T) -> R?
): List<T>

Returns a list of all elements sorted according to natural sort order of the value returned by specified selector function.

sortedByDescending

fun <T, R : Comparable<R>> Iterable<T>.sortedByDescending(
    selector: (T) -> R?
): List<T>

Returns a list of all elements sorted descending according to natural sort order of the value returned by specified selector function.

sortedDescending

fun <T : Comparable<T>> Iterable<T>.sortedDescending(): List<T>

Returns a list of all elements sorted descending according to their natural sort order.

sortedWith

fun <T> Iterable<T>.sortedWith(
    comparator: Comparator<in T>
): List<T>

fun <T> Iterable<T>.sortedWith(
    comparator: Comparator<in T>
): List<T>

Returns a list of all elements sorted according to the specified comparator.

subtract

infix fun <T> Iterable<T>.subtract(
    other: Iterable<T>
): Set<T>

Returns a set containing all elements that are contained by this collection and not contained by the specified collection.

sumBy

fun <T> Iterable<T>.sumBy(selector: (T) -> Int): Int

Returns the sum of all values produced by selector function applied to each element in the collection.

sumByDouble

fun <T> Iterable<T>.sumByDouble(
    selector: (T) -> Double
): Double

Returns the sum of all values produced by selector function applied to each element in the collection.

take

fun <T> Iterable<T>.take(n: Int): List<T>

Returns a list containing first n elements.

takeWhile

fun <T> Iterable<T>.takeWhile(
    predicate: (T) -> Boolean
): List<T>

Returns a list containing first elements satisfying the given predicate.

toCollection

fun <T, C : MutableCollection<in T>> Iterable<T>.toCollection(
    destination: C
): C

Appends all elements to the given destination collection.

toHashSet

fun <T> Iterable<T>.toHashSet(): HashSet<T>

Returns a HashSet of all elements.

toList

fun <T> Iterable<T>.toList(): List<T>

Returns a List containing all elements.

toMutableSet

fun <T> Iterable<T>.toMutableSet(): MutableSet<T>

Returns a mutable set containing all distinct elements from the given collection.

toSet

fun <T> Iterable<T>.toSet(): Set<T>

Returns a Set of all elements.

toSortedSet

fun <T : Comparable<T>> Iterable<T>.toSortedSet(): SortedSet<T>

fun <T> Iterable<T>.toSortedSet(
    comparator: Comparator<in T>
): SortedSet<T>

Returns a SortedSet of all elements.

toTypedArray

fun <T> Collection<T>.toTypedArray(): Array<T>

Returns a typed array containing all of the elements of this collection.

union

infix fun <T> Iterable<T>.union(other: Iterable<T>): Set<T>

Returns a set containing all distinct elements from both collections.

withIndex

fun <T> Iterable<T>.withIndex(): Iterable<IndexedValue<T>>

Returns a lazy Iterable of IndexedValue for each element of the original collection.

zip

infix fun <T, R> Iterable<T>.zip(
    other: Array<out R>
): List<Pair<T, R>>

infix fun <T, R> Iterable<T>.zip(
    other: Iterable<R>
): List<Pair<T, R>>

Returns a list of pairs built from elements of both collections with same indexes. List has length of shortest collection.

fun <T, R, V> Iterable<T>.zip(
    other: Array<out R>, 
    transform: (a: T, b: R) -> V
): List<V>

fun <T, R, V> Iterable<T>.zip(
    other: Iterable<R>, 
    transform: (a: T, b: R) -> V
): List<V>

Returns a list of values built from elements of both collections with same indexes using provided transform. List has length of shortest collection.

AbstractSet

abstract class AbstractSet<out E> : 
    AbstractCollection<E>, 
    Set<E>

Provides a skeletal implementation of the read-only Set interface.

MutableSet

interface MutableSet<E> : Set<E>, MutableCollection<E>

A generic unordered collection of elements that does not support duplicate elements, and supports adding and removing elements.