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.