Kotlin List mapTo()
Syntax & Examples

Syntax of List.mapTo()

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

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

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

✐ Examples

1 Example

In this example,

We create a list named list1 containing the integers 1, 2, 3.
We create an empty mutable list named destination to store the transformed elements.
We then apply the mapTo function to list1, which takes a lambda with one parameter: it.
Within the lambda, we double each element.
The mapTo function appends the transformed elements to the destination list.
The resulting list, containing doubled values of elements from list1, is stored in result.
Finally, we print the value of result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(1, 2, 3);
    val destination = mutableListOf<Int>();
    val result = list1.mapTo(destination) { it * 2 }
    print(result);
}

Output

[2, 4, 6]

2 Example

In this example,

We create a list named list1 containing the characters 'a', 'b', 'c'.
We create an empty mutable list named destination to store the transformed elements.
We then apply the mapTo function to list1, which takes a lambda with one parameter: it.
Within the lambda, we convert each character to uppercase.
The mapTo function appends the transformed elements to the destination list.
The resulting list, containing uppercase versions of characters from list1, 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;b&quot;, &quot;c&quot;);
    val destination = mutableListOf<String>();
    val result = list1.mapTo(destination) { it.toUpperCase() }
    print(result);
}

Output

[A, B, C]

3 Example

In this example,

We create a list named list1 containing the strings 'apple', 'banana', 'cherry'.
We create an empty mutable list named destination to store the transformed elements.
We then apply the mapTo function to list1, which takes a lambda with one parameter: it.
Within the lambda, we get the length of each string.
The mapTo function appends the transformed elements to the destination list.
The resulting list, containing the lengths of strings from list1, 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 destination = mutableListOf<Int>();
    val result = list1.mapTo(destination) { it.length }
    print(result);
}

Output

[5, 6, 6]

Summary

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