Kotlin List mapIndexed()
Syntax & Examples

Syntax of List.mapIndexed()

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

fun <T, R> Iterable<T>.mapIndexed( transform: (index: Int, T) -> R ): List<R>

This mapIndexed() extension function of List returns a list containing the results of applying the given transform function to each element and its index in the original collection.


✐ Examples

1 Example

In this example,

  • We create a list named list1 containing the integers 10, 20, 30.
  • We then apply the mapIndexed function to list1, which takes a lambda with two parameters: index and value.
  • Within the lambda, we concatenate the index and value into a string format.
  • The mapIndexed function returns a new list containing the transformed elements.
  • The resulting list, containing strings representing each element along with its index, is stored in result.
  • Finally, we print the value of result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(10, 20, 30);
    val result = list1.mapIndexed { index, value -> "\$index: \$value" }
    print(result);
}

Output

[0: 10, 1: 20, 2: 30]

2 Example

In this example,

  • We create a list named list1 containing the characters 'a', 'p', 'p', 'l', 'e'.
  • We then apply the mapIndexed function to list1, which takes a lambda with two parameters: index and value.
  • Within the lambda, we concatenate the index and value into a string format.
  • The mapIndexed function returns a new list containing the transformed elements.
  • The resulting list, containing strings representing each character along with its index, is stored in result.
  • Finally, we print the value of result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(&quot;a&quot;, &quot;p&quot;, &quot;p&quot;, &quot;l&quot;, &quot;e&quot;);
    val result = list1.mapIndexed { index, value -> "\$index: \$value" }
    print(result);
}

Output

[0: a, 1: p, 2: p, 3: l, 4: e]

3 Example

In this example,

  • We create a list named list1 containing the strings 'apple', 'banana', 'cherry'.
  • We then apply the mapIndexed function to list1, which takes a lambda with two parameters: index and value.
  • Within the lambda, we concatenate the index and value into a string format.
  • The mapIndexed function returns a new list containing the transformed elements.
  • The resulting list, containing strings representing each element along with its index, is stored in result.
  • Finally, we print the value of result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("apple", "banana", "cherry");
    val result = list1.mapIndexed { index, value -> "\$index: \$value" }
    print(result);
}

Output

[0: apple, 1: banana, 2: cherry]

Summary

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