kotlin-stdlib/kotlin.sequences/associateTo

associateTo

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

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

If any of two pairs would have the same key the last one gets added to the map.

The operation is terminal.

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.associateTo(byLastName) { it.lastName to 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
}