Kotlin List mapIndexedTo()
Syntax & Examples

Syntax of List.mapIndexedTo()

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

fun <T, R, C : MutableCollection<in R>> Iterable<T>.mapIndexedTo( destination: C, transform: (index: Int, T) -> R ): C

This mapIndexedTo() extension function of List applies the given transform function to each element and its index in the original collection and appends the results to the given destination.

✐ Examples

1 Example

In this example,

We create a list of integers named list containing elements 1, 2, 3, 4, 5.
We create a mutable destination list named destination.
We use the mapIndexedTo() function with an index and value.
We transform each element and index into a string format and append them to the destination list.
The resulting destination list, result, is printed to standard output using println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(1, 2, 3, 4, 5)
    val destination = mutableListOf<String>()
    val result = list.mapIndexedTo(destination) { index, value -> "Item \$index: \$value" }
    println("Mapped list: \$result")
}

Output

Mapped list: [Item 0: 1, Item 1: 2, Item 2: 3, Item 3: 4, Item 4: 5]

2 Example

In this example,

We create a list of characters named list containing elements 'a', 'b', 'c'.
We create a mutable destination list named destination.
We use the mapIndexedTo() function with an index and value.
We transform each character and its index into a string format and append them to the destination list.
The resulting destination list, result, is printed to standard output using println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf('a', 'b', 'c')
    val destination = mutableListOf<String>()
    val result = list.mapIndexedTo(destination) { index, value -> "Index \$index: \$value" }
    println("Mapped list: \$result")
}

Output

Mapped list: [Index 0: a, Index 1: b, Index 2: c]

3 Example

In this example,

We create a list of strings named list containing elements "apple", "banana", "cherry".
We create a mutable destination list named destination.
We use the mapIndexedTo() function with an index and value.
We transform each string and its index into a string format and append them to the destination list.
The resulting destination list, result, is printed to standard output using println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf("apple", "banana", "cherry")
    val destination = mutableListOf<String>()
    val result = list.mapIndexedTo(destination) { index, value -> "\$value is at index \$index" }
    println("Mapped list: \$result")
}

Output

Mapped list: [apple is at index 0, banana is at index 1, cherry is at index 2]

Summary

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