Kotlin Tutorials

Kotlin Set associateWithTo()
Syntax & Examples

Set.associateWithTo() extension function

The associateWithTo() extension function for sets in Kotlin populates and returns the destination mutable map with key-value pairs for each element of the set, where the key is the element itself and the value is provided by the valueSelector function applied to that key.

Syntax of Set.associateWithTo()

The syntax of Set.associateWithTo() extension function is:

fun <K, V, M : MutableMap<in K, in V>> Set<K>.associateWithTo(destination: M, valueSelector: (K) -> V): M

This associateWithTo() extension function of Set populates and returns the destination mutable map with key-value pairs for each element of the given set, where the key is the element itself and the value is provided by the valueSelector function applied to that key.

Parameters

ParameterOptional/RequiredDescription
destinationrequiredThe mutable map to which key-value pairs will be added.
valueSelectorrequiredA function that takes an element of the set and returns a value for the resulting map.

Return Type

Set.associateWithTo() returns value of type M.


✐ Examples

1 Using associateWithTo() to populate a mutable map with elements of a set of strings

In Kotlin, we can use the associateWithTo() function to populate a mutable map with elements from a set of strings, where the keys are the strings and the values are their lengths.

For example,

  1. Create a set of strings.
  2. Create an empty mutable map.
  3. Use the associateWithTo() function with a valueSelector function that returns the length of the string.
  4. Print the resulting map to the console using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val fruits = setOf("apple", "banana", "cherry")
    val fruitLengths = mutableMapOf<String, Int>()
    fruits.associateWithTo(fruitLengths) { it.length }
    println("Fruit lengths: $fruitLengths")
}

Output

Fruit lengths: {apple=5, banana=6, cherry=6}

2 Using associateWithTo() to populate a mutable map with elements of a set of integers

In Kotlin, we can use the associateWithTo() function to populate a mutable map with elements from a set of integers, where the keys are the integers and the values are their squares.

For example,

  1. Create a set of integers.
  2. Create an empty mutable map.
  3. Use the associateWithTo() function with a valueSelector function that returns the square of the integer.
  4. Print the resulting map to the console using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val numbers = setOf(1, 2, 3, 4, 5)
    val squaresMap = mutableMapOf<Int, Int>()
    numbers.associateWithTo(squaresMap) { it * it }
    println("Number squares: $squaresMap")
}

Output

Number squares: {1=1, 2=4, 3=9, 4=16, 5=25}

3 Using associateWithTo() with an empty set

In Kotlin, we can use the associateWithTo() function to populate a mutable map with elements from an empty set, which will result in an empty map.

For example,

  1. Create an empty set of integers.
  2. Create an empty mutable map.
  3. Use the associateWithTo() function with a valueSelector function that returns the square of the integer.
  4. Print the resulting map to the console using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val emptySet = emptySet<Int>()
    val squaresMap = mutableMapOf<Int, Int>()
    emptySet.associateWithTo(squaresMap) { it * it }
    println("Number squares in empty set: $squaresMap")
}

Output

Number squares in empty set: {}

Summary

In this Kotlin tutorial, we learned about associateWithTo() extension function of Set: the syntax and few working examples with output and detailed explanation for each example.