kotlin-stdlib / kotlin.collections / Map

Map

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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

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

V - the type of map values. The map is covariant on its value type.

Types

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Entry

Represents a key/value pair held by a Map.

interface Entry<out K, out V>

Properties

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entries

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

abstract val entries: Set<Entry<K, V>>
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keys

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

abstract val keys: Set<K>
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size

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

abstract val size: Int
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values

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

abstract val values: Collection<V>

Functions

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containsKey

Returns true if the map contains the specified key.

abstract fun containsKey(key: K): Boolean
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containsValue

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

abstract fun containsValue(value: V): Boolean
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get

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

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

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

open fun getOrDefault(key: K, defaultValue: V): V
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isEmpty

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

abstract fun isEmpty(): Boolean

Extension Functions

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all

Returns true if all entries match the given predicate.

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

Returns true if map has at least one entry.

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

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

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

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

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

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

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

Checks if the map contains the given key.

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

Returns true if the map contains the specified key.

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

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

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

Returns the number of entries in this map.

fun <K, V> Map<out K, V>.count(): Int

Returns the number of entries matching the given predicate.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Performs the given action on each entry.

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

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

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

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

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

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

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

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

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

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

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

Returns true if this map is not empty.

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

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

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

Returns an Iterator over the entries in the Map.

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

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

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

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.

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

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.

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

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

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

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

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

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

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

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.

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

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.

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

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

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

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

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

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

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

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(key: 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: 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 array.

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 sequence.

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

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

fun <K, V> Map<out K, V>.minWith(
    comparator: Comparator<in Entry<K, V>>
): Entry<K, V>?
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none

Returns true if the map has no entries.

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

Returns true if no entries match the given predicate.

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

Performs the given action on each entry and returns the map itself afterwards.

fun <K, V, M : Map<out K, V>> M.onEach(
    action: (Entry<K, V>) -> Unit
): M
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orEmpty

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

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

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(
    pair: 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: Iterable<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: 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 sequence 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 another map.

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

Returns a List containing all key-value pairs.

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

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

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

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

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

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

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

Converts this Map to a Properties object.

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

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

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 the sorting order provided by the given comparator.

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

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

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

Inheritors

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AbstractMap

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

abstract class AbstractMap<K, out V> : Map<K, V>
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MutableMap

A modifiable 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.

interface MutableMap<K, V> : Map<K, V>