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.