Kotlin Tutorials

Kotlin Set toMap()
Syntax & Examples

Set.toMap() extension function

The toMap() extension function in Kotlin returns a new map containing all key-value pairs from the given collection of pairs. It can also populate and return the destination mutable map with key-value pairs from the given collection of pairs.

Syntax of Set.toMap()

There are 2 variations for the syntax of Set.toMap() extension function. They are:

1.
fun <K, V> Iterable<Pair<K, V>>.toMap(): Map<K, V>

This extension function returns a new map containing all key-value pairs from the given collection of pairs.

Returns value of type Map<K, V>.

2.
fun <K, V, M : MutableMap<in K, in V>> Iterable<Pair<K, V>>.toMap(destination: M): M

This extension function populates and returns the destination mutable map with key-value pairs from the given collection of pairs.

Returns value of type M.


✐ Examples

1 Converting a set of pairs to a map

Using toMap() to convert a set of pairs to a map.

For example,

  1. Create a set of pairs.
  2. Use toMap() to convert the set to a map.
  3. Print the resulting map.

Kotlin Program

fun main() {
    val pairs = setOf(Pair("one", 1), Pair("two", 2), Pair("three", 3))
    val map = pairs.toMap()
    println(map)
}

Output

{one=1, two=2, three=3}

2 Populating a mutable map with key-value pairs from a set of pairs

Using toMap() to populate a mutable map with key-value pairs from a set of pairs.

For example,

  1. Create a set of pairs.
  2. Create a mutable map.
  3. Use toMap() to populate the mutable map with key-value pairs from the set of pairs.
  4. Print the resulting map.

Kotlin Program

fun main() {
    val pairs = setOf(Pair("one", 1), Pair("two", 2), Pair("three", 3))
    val destination = mutableMapOf<String, Int>()
    pairs.toMap(destination)
    println(destination)
}

Output

{one=1, two=2, three=3}

3 Converting a set of pairs with custom objects to a map

Using toMap() to convert a set of pairs with custom objects to a map.

For example,

  1. Create a data class.
  2. Create a set of pairs with custom objects.
  3. Use toMap() to convert the set to a map.
  4. Print the resulting map.

Kotlin Program

data class Person(val name: String, val age: Int)

fun main() {
    val pairs = setOf(Pair(Person("Alice", 30), 1), Pair(Person("Bob", 25), 2), Pair(Person("Charlie", 35), 3))
    val map = pairs.toMap()
    println(map)
}

Output

{Person(name=Alice, age=30)=1, Person(name=Bob, age=25)=2, Person(name=Charlie, age=35)=3}

Summary

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