Kotlin Tutorials

Kotlin Map onEachIndexed()
Syntax & Examples

Syntax of Map.onEachIndexed()

The syntax of Map.onEachIndexed() extension function is:

fun <K, V, M : Map<out K, V>> M.onEachIndexed( action: (index: Int, Entry<K, V>) -> Unit ): M

This onEachIndexed() extension function of Map performs the given action on each entry, providing sequential index with the entry, and returns the map itself afterwards.


✐ Examples

1 Print each entry with index in the map

In this example,

  • We create a map named map1 containing key-value pairs 1 to 'a', 2 to 'b', and 3 to 'c'.
  • We then apply the onEachIndexed() function on map1 to perform an action on each entry with its sequential index, in this case, printing the index, key, and value.
  • The function returns the map itself.

Kotlin Program

fun main(args: Array<String>) {
    val map1 = mapOf(1 to 'a', 2 to 'b', 3 to 'c');
    map1.onEachIndexed { index, entry -> println("Index: $index, Key: ${entry.key}, Value: ${entry.value}") }
}

Output

Index: 0, Key: 1, Value: a
Index: 1, Key: 2, Value: b
Index: 2, Key: 3, Value: c

2 Print each entry with index in the map

In this example,

  • We create a map named map2 containing key-value pairs 'a' to 1, 'b' to 2, and 'c' to 3.
  • We then apply the onEachIndexed() function on map2 to perform an action on each entry with its sequential index, in this case, printing the index, key, and value.
  • The function returns the map itself.

Kotlin Program

fun main(args: Array<String>) {
    val map2 = mapOf('a' to 1, 'b' to 2, 'c' to 3);
    map2.onEachIndexed { index, entry -> println("Index: $index, Key: ${entry.key}, Value: ${entry.value}") }
}

Output

Index: 0, Key: a, Value: 1
Index: 1, Key: b, Value: 2
Index: 2, Key: c, Value: 3

3 Print each entry with index in the map

In this example,

  • We create a map named map3 containing key-value pairs 1 to "apple", 2 to "banana", and 3 to "cherry".
  • We then apply the onEachIndexed() function on map3 to perform an action on each entry with its sequential index, in this case, printing the index, key, and value.
  • The function returns the map itself.

Kotlin Program

fun main(args: Array<String>) {
    val map3 = mapOf(1 to "apple", 2 to "banana", 3 to "cherry");
    map3.onEachIndexed { index, entry -> println("Index: $index, Key: ${entry.key}, Value: ${entry.value}") }
}

Output

Index: 0, Key: 1, Value: apple
Index: 1, Key: 2, Value: banana
Index: 2, Key: 3, Value: cherry

Summary

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