kotlin-stdlib/kotlin.collections/associateByTo

associateByTo

inline fun <T, K, M : MutableMap<in K, in T>> Array<out T>.associateByTo(destination: M, keySelector: (T) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Byte>> ByteArray.associateByTo(destination: M, keySelector: (Byte) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Short>> ShortArray.associateByTo(destination: M, keySelector: (Short) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Int>> IntArray.associateByTo(destination: M, keySelector: (Int) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Long>> LongArray.associateByTo(destination: M, keySelector: (Long) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Float>> FloatArray.associateByTo(destination: M, keySelector: (Float) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Double>> DoubleArray.associateByTo(destination: M, keySelector: (Double) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Boolean>> BooleanArray.associateByTo(destination: M, keySelector: (Boolean) -> K): M(source)

inline fun <K, M : MutableMap<in K, in Char>> CharArray.associateByTo(destination: M, keySelector: (Char) -> K): M(source)

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 array and value is the element itself.

If any two elements would have the same key returned by keySelector the last one gets added to the map.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   val charCodes = intArrayOf(72, 69, 76, 76, 79)
val byChar = mutableMapOf<Char, Int>()

println("byChar.isEmpty() is ${byChar.isEmpty()}") // true
charCodes.associateByTo(byChar) { Char(it) }

println("byChar.isNotEmpty() is ${byChar.isNotEmpty()}") // true
// L=76 only occurs once because only the last pair with the same key gets added
println(byChar) // {H=72, E=69, L=76, O=79} 
   //sampleEnd
}
xxxxxxxxxx
 
val charCodes = intArrayOf(72, 69, 76, 76, 79)
val byChar = mutableMapOf<Char, Int>()
println("byChar.isEmpty() is ${byChar.isEmpty()}") // true
charCodes.associateByTo(byChar) { Char(it) }
println("byChar.isNotEmpty() is ${byChar.isNotEmpty()}") // true
// L=76 only occurs once because only the last pair with the same key gets added
println(byChar) // {H=72, E=69, L=76, O=79} 
Open in Playground →
Target: JVMRunning on v.2.1.20

inline fun <T, K, V, M : MutableMap<in K, in V>> Array<out T>.associateByTo( destination: M, keySelector: (T) -> K, valueTransform: (T) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> ByteArray.associateByTo( destination: M, keySelector: (Byte) -> K, valueTransform: (Byte) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> ShortArray.associateByTo( destination: M, keySelector: (Short) -> K, valueTransform: (Short) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> IntArray.associateByTo(destination: M, keySelector: (Int) -> K, valueTransform: (Int) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> LongArray.associateByTo( destination: M, keySelector: (Long) -> K, valueTransform: (Long) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> FloatArray.associateByTo( destination: M, keySelector: (Float) -> K, valueTransform: (Float) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> DoubleArray.associateByTo( destination: M, keySelector: (Double) -> K, valueTransform: (Double) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> BooleanArray.associateByTo( destination: M, keySelector: (Boolean) -> K, valueTransform: (Boolean) -> V): M(source)

inline fun <K, V, M : MutableMap<in K, in V>> CharArray.associateByTo( destination: M, keySelector: (Char) -> K, valueTransform: (Char) -> V): M(source)

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 array.

If any two elements would have the same key returned by keySelector the last one gets added to the map.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   val charCodes = intArrayOf(65, 65, 66, 67, 68, 69)

val byUpperCase = mutableMapOf<Char, Char>()
charCodes.associateByTo(byUpperCase, { Char(it) }, { Char(it + 32) })

// A=a only occurs once because only the last pair with the same key gets added
println(byUpperCase) // {A=a, B=b, C=c, D=d, E=e} 
   //sampleEnd
}
xxxxxxxxxx
 
val charCodes = intArrayOf(65, 65, 66, 67, 68, 69)
val byUpperCase = mutableMapOf<Char, Char>()
charCodes.associateByTo(byUpperCase, { Char(it) }, { Char(it + 32) })
// A=a only occurs once because only the last pair with the same key gets added
println(byUpperCase) // {A=a, B=b, C=c, D=d, E=e} 
Open in Playground →
Target: JVMRunning on v.2.1.20

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

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.

If any two elements would have the same key returned by keySelector the last one gets added to the map.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   data class Person(val firstName: String, val lastName: String) {
    override fun toString(): String = "$firstName $lastName"
}

val scientists = listOf(Person("Grace", "Hopper"), Person("Jacob", "Bernoulli"), Person("Johann", "Bernoulli"))

val byLastName = mutableMapOf<String, Person>()
println("byLastName.isEmpty() is ${byLastName.isEmpty()}") // true

scientists.associateByTo(byLastName) { it.lastName }

println("byLastName.isNotEmpty() is ${byLastName.isNotEmpty()}") // true
// Jacob Bernoulli does not occur in the map because only the last pair with the same key gets added
println(byLastName) // {Hopper=Grace Hopper, Bernoulli=Johann Bernoulli} 
   //sampleEnd
}
xxxxxxxxxx
 
data class Person(val firstName: String, val lastName: String) {
    override fun toString(): String = "$firstName $lastName"
}
val scientists = listOf(Person("Grace", "Hopper"), Person("Jacob", "Bernoulli"), Person("Johann", "Bernoulli"))
val byLastName = mutableMapOf<String, Person>()
println("byLastName.isEmpty() is ${byLastName.isEmpty()}") // true
scientists.associateByTo(byLastName) { it.lastName }
println("byLastName.isNotEmpty() is ${byLastName.isNotEmpty()}") // true
// Jacob Bernoulli does not occur in the map because only the last pair with the same key gets added
println(byLastName) // {Hopper=Grace Hopper, Bernoulli=Johann Bernoulli} 
Open in Playground →
Target: JVMRunning on v.2.1.20

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

If any two elements would have the same key returned by keySelector the last one gets added to the map.

Since Kotlin

1.0

Samples

import kotlin.test.*

fun main() { 
   //sampleStart 
   data class Person(val firstName: String, val lastName: String)

val scientists = listOf(Person("Grace", "Hopper"), Person("Jacob", "Bernoulli"), Person("Johann", "Bernoulli"))

val byLastName = mutableMapOf<String, String>()
println("byLastName.isEmpty() is ${byLastName.isEmpty()}") // true

scientists.associateByTo(byLastName, { it.lastName }, { it.firstName} )

println("byLastName.isNotEmpty() is ${byLastName.isNotEmpty()}") // true
// Jacob Bernoulli does not occur in the map because only the last pair with the same key gets added
println(byLastName) // {Hopper=Grace, Bernoulli=Johann} 
   //sampleEnd
}
xxxxxxxxxx
 
data class Person(val firstName: String, val lastName: String)
val scientists = listOf(Person("Grace", "Hopper"), Person("Jacob", "Bernoulli"), Person("Johann", "Bernoulli"))
val byLastName = mutableMapOf<String, String>()
println("byLastName.isEmpty() is ${byLastName.isEmpty()}") // true
scientists.associateByTo(byLastName, { it.lastName }, { it.firstName} )
println("byLastName.isNotEmpty() is ${byLastName.isNotEmpty()}") // true
// Jacob Bernoulli does not occur in the map because only the last pair with the same key gets added
println(byLastName) // {Hopper=Grace, Bernoulli=Johann} 
Open in Playground →
Target: JVMRunning on v.2.1.20

Thanks for your feedback!

Was this page helpful?