Kotlin Map onEach()
Syntax & Examples

Syntax of Map.onEach()

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

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

This onEach() extension function of Map performs the given action on each entry and returns the map itself afterwards.

✐ Examples

1 Print each entry 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 onEach() function on map1 to perform an action on each entry, in this case, printing the 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.onEach { entry -> println("Key: ${entry.key}, Value: ${entry.value}") }
}

Output

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

2 Print each entry 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 onEach() function on map2 to perform an action on each entry, in this case, printing the 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.onEach { entry -> println("Key: ${entry.key}, Value: ${entry.value}") }
}

Output

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

3 Print each entry 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 onEach() function on map3 to perform an action on each entry, in this case, printing the 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.onEach { entry -> println("Key: ${entry.key}, Value: ${entry.value}") }
}

Output

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

Summary

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