kotlin-stdlib/kotlin.collections/[Native]Map

Map

interface Map<K, out V>

A collection that holds pairs of objects (keys and values) and supports efficiently retrieving the value corresponding to each key. Map keys are unique; the map holds only one value for each key. Methods in this interface support only read-only access to the map; read-write access is supported through the MutableMap interface.

Parameters

the type of map keys. The map is invariant in its key type, as it can accept key as a parameter (of containsKey for example) and return it in keys set.

the type of map values. The map is covariant in its value type.

Types

Entry

interface Entry<out K, out V>

Represents a key/value pair held by a Map.

Functions

containsKey

abstract fun containsKey(key: K): Boolean

Returns true if the map contains the specified key.

containsValue

abstract fun containsValue(value: @UnsafeVariance V): Boolean

Returns true if the map maps one or more keys to the specified value.

get

abstract operator fun get(key: K): V?

Returns the value corresponding to the given key, or null if such a key is not present in the map.

isEmpty

abstract fun isEmpty(): Boolean

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

Properties

entries

abstract val entries: Set<Map.Entry<K, V>>

Returns a read-only Set of all key/value pairs in this map.

keys

abstract val keys: Set<K>

Returns a read-only Set of all keys in this map.

size

abstract val size: Int

Returns the number of key/value pairs in the map.

values

abstract val values: Collection<V>

Returns a read-only Collection of all values in this map. Note that this collection may contain duplicate values.

Inheritors

AbstractMap

MutableMap

Extensions

all

inline fun <K, V> Map<out K, V>.all(predicate: (Map.Entry<K, V>) -> Boolean): Boolean

Returns true if all entries match the given predicate.

any

fun <K, V> Map<out K, V>.any(): Boolean

Returns true if map has at least one entry.

inline fun <K, V> Map<out K, V>.any(predicate: (Map.Entry<K, V>) -> Boolean): Boolean

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

asIterable

inline fun <K, V> Map<out K, V>.asIterable(): Iterable<Map.Entry<K, V>>

Creates an Iterable instance that wraps the original map returning its entries when being iterated.

asSequence

fun <K, V> Map<out K, V>.asSequence(): Sequence<Map.Entry<K, V>>

Creates a Sequence instance that wraps the original map returning its entries when being iterated.

contains

inline operator fun <K, V> Map<out K, V>.contains(key: K): Boolean

Checks if the map contains the given key.

containsKey

inline fun <K> Map<out K, *>.containsKey(key: K): Boolean

Returns true if the map contains the specified key.

containsValue

inline fun <K, V> Map<K, V>.containsValue(value: V): Boolean

Returns true if the map maps one or more keys to the specified value.

count

inline fun <K, V> Map<out K, V>.count(): Int

Returns the number of entries in this map.

inline fun <K, V> Map<out K, V>.count(predicate: (Map.Entry<K, V>) -> Boolean): Int

Returns the number of entries matching the given predicate.

filter

inline fun <K, V> Map<out K, V>.filter(predicate: (Map.Entry<K, V>) -> Boolean): Map<K, V>

Returns a new map containing all key-value pairs matching the given predicate.

filterKeys

inline fun <K, V> Map<out K, V>.filterKeys(predicate: (K) -> Boolean): Map<K, V>

Returns a map containing all key-value pairs with keys matching the given predicate.

filterNot

inline fun <K, V> Map<out K, V>.filterNot(predicate: (Map.Entry<K, V>) -> Boolean): Map<K, V>

Returns a new map containing all key-value pairs not matching the given predicate.

filterNotTo

inline fun <K, V, M : MutableMap<in K, in V>> Map<out K, V>.filterNotTo(destination: M, predicate: (Map.Entry<K, V>) -> Boolean): M

Appends all entries not matching the given predicate into the given destination.

filterTo

inline fun <K, V, M : MutableMap<in K, in V>> Map<out K, V>.filterTo(destination: M, predicate: (Map.Entry<K, V>) -> Boolean): M

Appends all entries matching the given predicate into the mutable map given as destination parameter.

filterValues

inline fun <K, V> Map<out K, V>.filterValues(predicate: (V) -> Boolean): Map<K, V>

Returns a map containing all key-value pairs with values matching the given predicate.

firstNotNullOf

inline fun <K, V, R : Any> Map<out K, V>.firstNotNullOf(transform: (Map.Entry<K, V>) -> R?): R

Returns the first non-null value produced by transform function being applied to entries of this map in iteration order, or throws NoSuchElementException if no non-null value was produced.

firstNotNullOfOrNull

inline fun <K, V, R : Any> Map<out K, V>.firstNotNullOfOrNull(transform: (Map.Entry<K, V>) -> R?): R?

Returns the first non-null value produced by transform function being applied to entries of this map in iteration order, or null if no non-null value was produced.

flatMap

inline fun <K, V, R> Map<out K, V>.flatMap(transform: (Map.Entry<K, V>) -> Iterable<R>): List<R>

@JvmName(name = "flatMapSequence")

inline fun <K, V, R> Map<out K, V>.flatMap(transform: (Map.Entry<K, V>) -> Sequence<R>): List<R>

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

flatMapTo

inline fun <K, V, R, C : MutableCollection<in R>> Map<out K, V>.flatMapTo(destination: C, transform: (Map.Entry<K, V>) -> Iterable<R>): C

@JvmName(name = "flatMapSequenceTo")

inline fun <K, V, R, C : MutableCollection<in R>> Map<out K, V>.flatMapTo(destination: C, transform: (Map.Entry<K, V>) -> Sequence<R>): C

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

forEach

inline fun <K, V> Map<out K, V>.forEach(action: (Map.Entry<K, V>) -> Unit)

Performs the given action on each entry.

get

inline operator fun <K, V> Map<out K, V>.get(key: K): V?

Returns the value corresponding to the given key, or null if such a key is not present in the map.

getOrDefault

inline fun <K, V> Map<out K, V>.getOrDefault(key: K, defaultValue: V): V

Returns the value to which the specified key is mapped, or defaultValue if this map contains no mapping for the key.

getOrElse

inline fun <K, V> Map<K, V>.getOrElse(key: K, defaultValue: () -> V): V

Returns the value for the given key, or the result of the defaultValue function if there was no entry for the given key.

getValue

inline operator fun <V, V1 : V> Map<in String, V>.getValue(thisRef: Any?, property: KProperty<*>): V1

Returns the value of the property for the given object from this read-only map.

fun <K, V> Map<K, V>.getValue(key: K): V

Returns the value for the given key or throws an exception if there is no such key in the map.

isNotEmpty

inline fun <K, V> Map<out K, V>.isNotEmpty(): Boolean

Returns true if this map is not empty.

isNullOrEmpty

inline fun <K, V> Map<out K, V>?.isNullOrEmpty(): Boolean

Returns true if this nullable map is either null or empty.

iterator

inline operator fun <K, V> Map<out K, V>.iterator(): Iterator<Map.Entry<K, V>>

Returns an Iterator over the entries in the Map.

map

inline fun <K, V, R> Map<out K, V>.map(transform: (Map.Entry<K, V>) -> R): List<R>

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

mapKeys

inline fun <K, V, R> Map<out K, V>.mapKeys(transform: (Map.Entry<K, V>) -> R): Map<R, V>

Returns a new Map with entries having the keys obtained by applying the transform function to each entry in this Map and the values of this map.

mapKeysTo

inline fun <K, V, R, M : MutableMap<in R, in V>> Map<out K, V>.mapKeysTo(destination: M, transform: (Map.Entry<K, V>) -> R): M

Populates the given destination map with entries having the keys obtained by applying the transform function to each entry in this Map and the values of this map.

mapNotNull

inline fun <K, V, R : Any> Map<out K, V>.mapNotNull(transform: (Map.Entry<K, V>) -> R?): List<R>

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

mapNotNullTo

inline fun <K, V, R : Any, C : MutableCollection<in R>> Map<out K, V>.mapNotNullTo(destination: C, transform: (Map.Entry<K, V>) -> R?): C

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

mapTo

inline fun <K, V, R, C : MutableCollection<in R>> Map<out K, V>.mapTo(destination: C, transform: (Map.Entry<K, V>) -> R): C

Applies the given transform function to each entry of the original map and appends the results to the given destination.

mapValues

inline fun <K, V, R> Map<out K, V>.mapValues(transform: (Map.Entry<K, V>) -> R): Map<K, R>

Returns a new map with entries having the keys of this map and the values obtained by applying the transform function to each entry in this Map.

mapValuesTo

inline fun <K, V, R, M : MutableMap<in K, in R>> Map<out K, V>.mapValuesTo(destination: M, transform: (Map.Entry<K, V>) -> R): M

Populates the given destination map with entries having the keys of this map and the values obtained by applying the transform function to each entry in this Map.

maxBy

@DeprecatedSinceKotlin(warningSince = "1.4", errorSince = "1.5")

~~inline~~ ~~fun~~ <K, V, R : Comparable<R>> Map<out K, V>.~~maxBy~~(~~selector~~: (Map.Entry<K, V>) -> R): Map.Entry<K, V>?

maxByOrNull

inline fun <K, V, R : Comparable<R>> Map<out K, V>.maxByOrNull(selector: (Map.Entry<K, V>) -> R): Map.Entry<K, V>?

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

maxOf

inline fun <K, V> Map<out K, V>.maxOf(selector: (Map.Entry<K, V>) -> Double): Double

inline fun <K, V> Map<out K, V>.maxOf(selector: (Map.Entry<K, V>) -> Float): Float

inline fun <K, V, R : Comparable<R>> Map<out K, V>.maxOf(selector: (Map.Entry<K, V>) -> R): R

Returns the largest value among all values produced by selector function applied to each entry in the map.

maxOfOrNull

inline fun <K, V> Map<out K, V>.maxOfOrNull(selector: (Map.Entry<K, V>) -> Double): Double?

inline fun <K, V> Map<out K, V>.maxOfOrNull(selector: (Map.Entry<K, V>) -> Float): Float?

inline fun <K, V, R : Comparable<R>> Map<out K, V>.maxOfOrNull(selector: (Map.Entry<K, V>) -> R): R?

Returns the largest value among all values produced by selector function applied to each entry in the map or null if there are no entries.

maxOfWith

inline fun <K, V, R> Map<out K, V>.maxOfWith(comparator: Comparator<in R>, selector: (Map.Entry<K, V>) -> R): R

Returns the largest value according to the provided comparator among all values produced by selector function applied to each entry in the map.

maxOfWithOrNull

inline fun <K, V, R> Map<out K, V>.maxOfWithOrNull(comparator: Comparator<in R>, selector: (Map.Entry<K, V>) -> R): R?

Returns the largest value according to the provided comparator among all values produced by selector function applied to each entry in the map or null if there are no entries.

maxWith

@DeprecatedSinceKotlin(warningSince = "1.4", errorSince = "1.5")

~~inline~~ ~~fun~~ <K, V> Map<out K, V>.~~maxWith~~(~~comparator~~: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?

maxWithOrNull

inline fun <K, V> Map<out K, V>.maxWithOrNull(comparator: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?

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

minBy

@DeprecatedSinceKotlin(warningSince = "1.4", errorSince = "1.5")

~~inline~~ ~~fun~~ <K, V, R : Comparable<R>> Map<out K, V>.~~minBy~~(~~selector~~: (Map.Entry<K, V>) -> R): Map.Entry<K, V>?

minByOrNull

inline fun <K, V, R : Comparable<R>> Map<out K, V>.minByOrNull(selector: (Map.Entry<K, V>) -> R): Map.Entry<K, V>?

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

minOf

inline fun <K, V> Map<out K, V>.minOf(selector: (Map.Entry<K, V>) -> Double): Double

inline fun <K, V> Map<out K, V>.minOf(selector: (Map.Entry<K, V>) -> Float): Float

inline fun <K, V, R : Comparable<R>> Map<out K, V>.minOf(selector: (Map.Entry<K, V>) -> R): R

Returns the smallest value among all values produced by selector function applied to each entry in the map.

minOfOrNull

inline fun <K, V> Map<out K, V>.minOfOrNull(selector: (Map.Entry<K, V>) -> Double): Double?

inline fun <K, V> Map<out K, V>.minOfOrNull(selector: (Map.Entry<K, V>) -> Float): Float?

inline fun <K, V, R : Comparable<R>> Map<out K, V>.minOfOrNull(selector: (Map.Entry<K, V>) -> R): R?

Returns the smallest value among all values produced by selector function applied to each entry in the map or null if there are no entries.

minOfWith

inline fun <K, V, R> Map<out K, V>.minOfWith(comparator: Comparator<in R>, selector: (Map.Entry<K, V>) -> R): R

Returns the smallest value according to the provided comparator among all values produced by selector function applied to each entry in the map.

minOfWithOrNull

inline fun <K, V, R> Map<out K, V>.minOfWithOrNull(comparator: Comparator<in R>, selector: (Map.Entry<K, V>) -> R): R?

Returns the smallest value according to the provided comparator among all values produced by selector function applied to each entry in the map or null if there are no entries.

minus

operator fun <K, V> Map<out K, V>.minus(key: K): Map<K, V>

Returns a map containing all entries of the original map except the entry with the given key.

operator fun <K, V> Map<out K, V>.minus(keys: Iterable<K>): Map<K, V>

Returns a map containing all entries of the original map except those entries the keys of which are contained in the given keys collection.

operator fun <K, V> Map<out K, V>.minus(keys: Array<out K>): Map<K, V>

Returns a map containing all entries of the original map except those entries the keys of which are contained in the given keys array.

operator fun <K, V> Map<out K, V>.minus(keys: Sequence<K>): Map<K, V>

Returns a map containing all entries of the original map except those entries the keys of which are contained in the given keys sequence.

minWith

@DeprecatedSinceKotlin(warningSince = "1.4", errorSince = "1.5")

~~fun~~ <K, V> Map<out K, V>.~~minWith~~(~~comparator~~: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?

minWithOrNull

inline fun <K, V> Map<out K, V>.minWithOrNull(comparator: Comparator<in Map.Entry<K, V>>): Map.Entry<K, V>?

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

none

fun <K, V> Map<out K, V>.none(): Boolean

Returns true if the map has no entries.

inline fun <K, V> Map<out K, V>.none(predicate: (Map.Entry<K, V>) -> Boolean): Boolean

Returns true if no entries match the given predicate.

orEmpty

inline fun <K, V> Map<K, V>?.orEmpty(): Map<K, V>

Returns the Map if its not null, or the empty Map otherwise.

plus

operator fun <K, V> Map<out K, V>.plus(pair: Pair<K, V>): Map<K, V>

Creates a new read-only map by replacing or adding an entry to this map from a given key-value pair.

operator fun <K, V> Map<out K, V>.plus(pairs: Iterable<Pair<K, V>>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from a given collection of key-value pairs.

operator fun <K, V> Map<out K, V>.plus(pairs: Array<out Pair<K, V>>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from a given array of key-value pairs.

operator fun <K, V> Map<out K, V>.plus(pairs: Sequence<Pair<K, V>>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from a given sequence of key-value pairs.

operator fun <K, V> Map<out K, V>.plus(map: Map<out K, V>): Map<K, V>

Creates a new read-only map by replacing or adding entries to this map from another map.

toList

fun <K, V> Map<out K, V>.toList(): List<Pair<K, V>>

Returns a List containing all key-value pairs.

toMap

fun <K, V> Map<out K, V>.toMap(): Map<K, V>

Returns a new read-only map containing all key-value pairs from the original map.

fun <K, V, M : MutableMap<in K, in V>> Map<out K, V>.toMap(destination: M): M

Populates and returns the destination mutable map with key-value pairs from the given map.

toMutableMap

fun <K, V> Map<out K, V>.toMutableMap(): MutableMap<K, V>

Returns a new mutable map containing all key-value pairs from the original map.

toProperties

inline fun Map<String, String>.toProperties(): Properties

Converts this Map to a Properties object.

toSortedMap

fun <K : Comparable<K>, V> Map<out K, V>.toSortedMap(): SortedMap<K, V>

Converts this Map to a SortedMap. The resulting SortedMap determines the equality and order of keys according to their natural sorting order.

fun <K, V> Map<out K, V>.toSortedMap(comparator: Comparator<in K>): SortedMap<K, V>

Converts this Map to a SortedMap. The resulting SortedMap determines the equality and order of keys according to the sorting order provided by the given comparator.

withDefault

fun <K, V> Map<K, V>.withDefault(defaultValue: (K) -> V): Map<K, V>

Returns a wrapper of this read-only map, having the implicit default value provided with the specified function defaultValue.