Collection
interface Collection<out E> : Iterable<E>A generic collection of elements. Methods in this interface support only read-only access to the collection; read/write access is supported through the MutableCollection interface.
Parameters
E - the type of elements contained in the collection. The collection is covariant on its element type.
Properties
size
Returns the size of the collection.
abstract val size: IntFunctions
contains
Checks if the specified element is contained in this collection.
abstract operator fun contains(element: E): BooleancontainsAll
Checks if all elements in the specified collection are contained in this collection.
abstract fun containsAll(elements: Collection<E>): BooleanisEmpty
Returns true if the collection is empty (contains no elements), false otherwise.
abstract fun isEmpty(): BooleanExtension Properties
indices
Returns an IntRange of the valid indices for this collection.
val Collection<*>.indices: IntRangeExtension Functions
associateBy
Returns a Map containing the elements from the given collection indexed by the key returned from keySelector function applied to each element.
Returns a Map containing the values provided by valueTransform and indexed by keySelector functions applied to elements of the given collection.
associateByTo
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, M : MutableMap<in K, in T>> Iterable<T>.associateByTo(
destination: M,
keySelector: (T) -> K
): MPopulates 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.
fun <T, K, V, M : MutableMap<in K, in V>> Iterable<T>.associateByTo(
destination: M,
keySelector: (T) -> K,
valueTransform: (T) -> V
): MassociateTo
Populates and returns the destination mutable map with key-value pairs provided by transform function applied to each element of the given collection.
fun <T, K, V, M : MutableMap<in K, in V>> Iterable<T>.associateTo(
destination: M,
transform: (T) -> Pair<K, V>
): MassociateWith
Returns a Map where keys are elements from the given collection and values are produced by the valueSelector function applied to each element.
associateWithTo
Populates and returns the destination mutable map with key-value pairs for each element of the given collection, where key is the element itself and value is provided by the valueSelector function applied to that key.
fun <K, V, M : MutableMap<in K, in V>> Iterable<K>.associateWithTo(
destination: M,
valueSelector: (K) -> V
): McontainsAll
Checks if all elements in the specified collection are contained in this collection.
fun <T> Collection<T>.containsAll(
elements: Collection<T>
): Booleancount
Returns the number of elements in this collection.
fun <T> Collection<T>.count(): IntelementAt
Returns an element at the given index or throws an IndexOutOfBoundsException if the index is out of bounds of this collection.
fun <T> Iterable<T>.elementAt(index: Int): TelementAtOrElse
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.
fun <T> Iterable<T>.elementAtOrElse(
index: Int,
defaultValue: (Int) -> T
): TfilterIndexedTo
Appends all elements matching the given predicate to the given destination.
fun <T, C : MutableCollection<in T>> Iterable<T>.filterIndexedTo(
destination: C,
predicate: (index: Int, T) -> Boolean
): CfilterIsInstance
Returns a list containing all elements that are instances of specified type parameter R.
filterIsInstanceTo
Appends all elements that are instances of specified type parameter R to the given destination.
fun <R, C : MutableCollection<in R>> Iterable<*>.filterIsInstanceTo(
destination: C
): CAppends all elements that are instances of specified class to the given destination.
fun <C : MutableCollection<in R>, R> Iterable<*>.filterIsInstanceTo(
destination: C,
klass: Class<R>
): CfilterNotNullTo
Appends all elements that are not null to the given destination.
fun <C : MutableCollection<in T>, T : Any> Iterable<T?>.filterNotNullTo(
destination: C
): CfilterNotTo
Appends all elements not matching the given predicate to the given destination.
fun <T, C : MutableCollection<in T>> Iterable<T>.filterNotTo(
destination: C,
predicate: (T) -> Boolean
): CfilterTo
Appends all elements matching the given predicate to the given destination.
fun <T, C : MutableCollection<in T>> Iterable<T>.filterTo(
destination: C,
predicate: (T) -> Boolean
): CfirstOrNull
Returns the first element, or null if the collection is empty.
fun <T> Iterable<T>.firstOrNull(): T?flatMapTo
Appends all elements yielded from results of transform function being invoked on each element of original collection, to the given destination.
fun <T, R, C : MutableCollection<in R>> Iterable<T>.flatMapTo(
destination: C,
transform: (T) -> Iterable<R>
): CgroupBy
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.
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
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, M : MutableMap<in K, MutableList<T>>> Iterable<T>.groupByTo(
destination: M,
keySelector: (T) -> K
): MGroups 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.
fun <T, K, V, M : MutableMap<in K, MutableList<V>>> Iterable<T>.groupByTo(
destination: M,
keySelector: (T) -> K,
valueTransform: (T) -> V
): MgroupingBy
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.
isNotEmpty
Returns true if the collection is not empty.
fun <T> Collection<T>.isNotEmpty(): BooleanisNullOrEmpty
Returns true if this nullable collection is either null or empty.
fun <T> Collection<T>?.isNullOrEmpty(): BooleanjoinTo
Appends the string from all the elements separated using separator and using the given prefix and postfix if supplied.
fun <T, A : Appendable> Iterable<T>.joinTo(
buffer: A,
separator: CharSequence = ", ",
prefix: CharSequence = "",
postfix: CharSequence = "",
limit: Int = -1,
truncated: CharSequence = "...",
transform: ((T) -> CharSequence)? = null
): AjoinToString
Creates a string from all the elements separated using separator and using the given prefix and postfix if supplied.
fun <T> Iterable<T>.joinToString(
separator: CharSequence = ", ",
prefix: CharSequence = "",
postfix: CharSequence = "",
limit: Int = -1,
truncated: CharSequence = "...",
transform: ((T) -> CharSequence)? = null
): StringlastOrNull
Returns the last element, or null if the collection is empty.
fun <T> Iterable<T>.lastOrNull(): T?mapIndexedNotNullTo
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.
fun <T, R : Any, C : MutableCollection<in R>> Iterable<T>.mapIndexedNotNullTo(
destination: C,
transform: (index: Int, T) -> R?
): CmapIndexedTo
Applies the given transform function to each element and its index in the original collection and appends the results to the given destination.
fun <T, R, C : MutableCollection<in R>> Iterable<T>.mapIndexedTo(
destination: C,
transform: (index: Int, T) -> R
): CmapNotNullTo
Applies the given transform function to each element in the original collection and appends only the non-null results to the given destination.
fun <T, R : Any, C : MutableCollection<in R>> Iterable<T>.mapNotNullTo(
destination: C,
transform: (T) -> R?
): CmapTo
Applies the given transform function to each element of the original collection and appends the results to the given destination.
fun <T, R, C : MutableCollection<in R>> Iterable<T>.mapTo(
destination: C,
transform: (T) -> R
): CmaxBy
Returns the first element yielding the largest value of the given function or null if there are no elements.
fun <T, R : Comparable<R>> Iterable<T>.maxBy(
selector: (T) -> R
): T?maxWith
Returns the first element having the largest value according to the provided comparator or null if there are no elements.
fun <T> Iterable<T>.maxWith(comparator: Comparator<in T>): T?minBy
Returns the first element yielding the smallest value of the given function or null if there are no elements.
fun <T, R : Comparable<R>> Iterable<T>.minBy(
selector: (T) -> R
): T?minus
Returns a list containing all elements of the original collection without the first occurrence of the given element.
Returns a list containing all elements of the original collection except the elements contained in the given elements array.
Returns a list containing all elements of the original collection except the elements contained in the given elements collection.
minWith
Returns the first element having the smallest value according to the provided comparator or null if there are no elements.
fun <T> Iterable<T>.minWith(comparator: Comparator<in T>): T?orEmpty
Returns this Collection if it's not null and the empty list otherwise.
fun <T> Collection<T>?.orEmpty(): Collection<T>plus
Returns a list containing all elements of the original collection and then the given element.
operator fun <T> Collection<T>.plus(element: 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> 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 collection.
operator fun <T> Collection<T>.plus(
elements: Iterable<T>
): List<T>plusElement
Returns a list containing all elements of the original collection and then the given element.
fun <T> Collection<T>.plusElement(element: T): List<T>random
Returns a random element from this collection.
fun <T> Collection<T>.random(): TReturns a random element from this collection using the specified source of randomness.
fun <T> Collection<T>.random(random: Random): TrandomOrNull
Returns a random element from this collection, or null if this collection is empty.
fun <T> Collection<T>.randomOrNull(): T?Returns a random element from this collection using the specified source of randomness, or null if this collection is empty.
fun <T> Collection<T>.randomOrNull(random: Random): T?requireNoNulls
Returns an original collection containing all the non-null elements, throwing an IllegalArgumentException if there are any null elements.
scanIndexed
scanReduceIndexed
Returns a list containing successive accumulation values generated by applying operation from left to right to each element, its index in the original collection and current accumulator value that starts with the first element of this collection.
single
Returns the single element, or throws an exception if the collection is empty or has more than one element.
fun <T> Iterable<T>.single(): TsingleOrNull
Returns single element, or null if the collection is empty or has more than one element.
fun <T> Iterable<T>.singleOrNull(): T?sortedBy
Returns a list of all elements sorted according to natural sort order of the value returned by specified selector function.
fun <T, R : Comparable<R>> Iterable<T>.sortedBy(
selector: (T) -> R?
): List<T>sortedByDescending
Returns a list of all elements sorted descending according to natural sort order of the value returned by specified selector function.
fun <T, R : Comparable<R>> Iterable<T>.sortedByDescending(
selector: (T) -> R?
): List<T>sortedWith
Returns a list of all elements sorted according to the specified comparator.
fun <T> Iterable<T>.sortedWith(
comparator: Comparator<in T>
): List<T>toBooleanArray
Returns an array of Boolean containing all of the elements of this collection.
fun Collection<Boolean>.toBooleanArray(): BooleanArraytoByteArray
Returns an array of Byte containing all of the elements of this collection.
fun Collection<Byte>.toByteArray(): ByteArraytoCharArray
Returns an array of Char containing all of the elements of this collection.
fun Collection<Char>.toCharArray(): CharArraytoCollection
Appends all elements to the given destination collection.
fun <T, C : MutableCollection<in T>> Iterable<T>.toCollection(
destination: C
): CtoDoubleArray
Returns an array of Double containing all of the elements of this collection.
fun Collection<Double>.toDoubleArray(): DoubleArraytoFloatArray
Returns an array of Float containing all of the elements of this collection.
fun Collection<Float>.toFloatArray(): FloatArraytoIntArray
Returns an array of Int containing all of the elements of this collection.
fun Collection<Int>.toIntArray(): IntArraytoLongArray
Returns an array of Long containing all of the elements of this collection.
fun Collection<Long>.toLongArray(): LongArraytoMap
Returns a new map containing all key-value pairs from the given collection of pairs.
Populates and returns the destination mutable map with key-value pairs from the given collection of pairs.
fun <K, V, M : MutableMap<in K, in V>> Iterable<Pair<K, V>>.toMap(
destination: M
): MtoMutableList
Returns a MutableList filled with all elements of this collection.
fun <T> Collection<T>.toMutableList(): MutableList<T>toMutableSet
Returns a mutable set containing all distinct elements from the given collection.
fun <T> Iterable<T>.toMutableSet(): MutableSet<T>toShortArray
Returns an array of Short containing all of the elements of this collection.
fun Collection<Short>.toShortArray(): ShortArraytoSortedSet
Returns a SortedSet of all elements.
fun <T> Iterable<T>.toSortedSet(
comparator: Comparator<in T>
): SortedSet<T>toUByteArray
Returns an array of UByte containing all of the elements of this collection.
fun Collection<UByte>.toUByteArray(): UByteArraytoUIntArray
Returns an array of UInt containing all of the elements of this collection.
fun Collection<UInt>.toUIntArray(): UIntArraytoULongArray
Returns an array of ULong containing all of the elements of this collection.
fun Collection<ULong>.toULongArray(): ULongArraytoUShortArray
Returns an array of UShort containing all of the elements of this collection.
fun Collection<UShort>.toUShortArray(): UShortArraywaitForMultipleFutures
fun <T> Collection<Future<T>>.waitForMultipleFutures(
millis: Int
): Set<Future<T>>windowed
Returns a list of snapshots of the window of the given size sliding along this collection with the given step, where each snapshot is a list.
withIndex
Returns a lazy Iterable that wraps each element of the original collection into an IndexedValue containing the index of that element and the element itself.
fun <T> Iterable<T>.withIndex(): Iterable<IndexedValue<T>>zip
Returns a list of pairs built from the elements of this collection and the other array with the same index.
The returned list has length of the shortest collection.
Returns a list of values built from the elements of this collection and the other array with the same index
using the provided transform function applied to each pair of elements.
The returned list has length of the shortest collection.
Returns a list of pairs built from the elements of this collection and other collection with the same index.
The returned list has length of the shortest collection.
zipWithNext
Returns a list of pairs of each two adjacent elements in this collection.
Inheritors
AbstractCollection
Provides a skeletal implementation of the read-only Collection interface.
abstract class AbstractCollection<out E> : Collection<E>List
A generic ordered collection of elements. Methods in this interface support only read-only access to the list; read/write access is supported through the MutableList interface.
interface List<out E> : Collection<E>MatchGroupCollection
Represents a collection of captured groups in a single match of a regular expression.
interface MatchGroupCollection : Collection<MatchGroup?>MutableCollection
A generic collection of elements that supports adding and removing elements.
interface MutableCollection<E> :
Collection<E>,
MutableIterable<E>Set
A generic unordered collection of elements that does not support duplicate elements. Methods in this interface support only read-only access to the set; read/write access is supported through the MutableSet interface.
interface Set<out E> : Collection<E>UByteArray
class UByteArray : Collection<UByte>UIntArray
class UIntArray : Collection<UInt>ULongArray
class ULongArray : Collection<ULong>UShortArray
class UShortArray : Collection<UShort>