Kotlin List associate()
Syntax & Examples

Syntax of List.associate()

The syntax of List.associate() extension function is:

fun <T, K, V> Iterable<T>.associate( transform: (T) -> Pair<K, V> ): Map<K, V>

This associate() extension function of List returns a Map containing key-value pairs provided by transform function applied to elements of the given collection.


✐ Examples

1 Example

In this example,

  • We create a list named list1 containing integers from 1 to 5.
  • We use the associate() function with a transform lambda that maps each element it to a Pair of it and it * 2.
  • The resulting map contains key-value pairs where each number is associated with its double value.
  • We print the map, which contains {1=2, 2=4, 3=6, 4=8, 5=10}.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(1, 2, 3, 4, 5);
    val map = list1.associate { it to it * 2 };
    println(map);
}

Output

{1=2, 2=4, 3=6, 4=8, 5=10}

2 Example

In this example,

  • We create a list named list2 containing characters 'a' to 'c'.
  • We use the associate() function with a transform lambda that maps each character it to a Pair of it and it.toUpperCase().
  • The resulting map contains key-value pairs where each lowercase character is associated with its uppercase equivalent.
  • We print the map, which contains {'a'='A', 'b'='B', 'c'='C'}.

Kotlin Program

fun main(args: Array<String>) {
    val list2 = listOf('a', 'b', 'c');
    val map = list2.associate { it to it.toUpperCase() };
    println(map);
}

Output

{a=A, b=B, c=C}

3 Example

In this example,

  • We create a list named list3 containing strings "apple", "banana", and "cherry".
  • We use the associate() function with a transform lambda that maps each string it to a Pair of its length and it.toUpperCase().
  • The resulting map contains key-value pairs where each string length is associated with its uppercase version.
  • We print the map, which contains {5='APPLE', 6='BANANA', 6='CHERRY'}.

Kotlin Program

fun main(args: Array<String>) {
    val list3 = listOf("apple", "banana", "cherry");
    val map = list3.associate { it.length to it.toUpperCase() };
    println(map);
}

Output

{5=APPLE, 6=CHERRY}

Summary

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