Kotlin List filterTo()
Syntax & Examples

Syntax of List.filterTo()

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

fun <T, C : MutableCollection<in T>> Iterable<T>.filterTo( destination: C, predicate: (T) -> Boolean ): C

This filterTo() extension function of List appends all elements matching the given predicate to the given destination.

✐ Examples

1 Example

In this example,

We create a list named list containing integers.
We create an empty mutable list named result to store the filtered elements.
We apply the filterTo extension function on list to filter out even numbers and append them to result.
Finally, we print the result list to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(1, 2, 3, 4, 5);
    val result = mutableListOf<Int>();
    list.filterTo(result) { it % 2 == 0 };
    println(result);
}

Output

[2, 4]

2 Example

In this example,

We create a list named list containing characters.
We create an empty mutable list named result to store the filtered elements.
We apply the filterTo extension function on list to filter out characters 'a' and 'e' and append them to result.
Finally, we print the result list to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf('a', 'b', 'c', 'd', 'e');
    val result = mutableListOf<Char>();
    list.filterTo(result) { it in listOf('a', 'e') };
    println(result);
}

Output

[a, e]

3 Example

In this example,

We create a list named list containing strings.
We create an empty mutable list named result to store the filtered elements.
We apply the filterTo extension function on list to filter out strings with a length greater than 5 and append them to result.
Finally, we print the result list to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf("apple", "banana", "orange", "kiwi", "mango");
    val result = mutableListOf<String>();
    list.filterTo(result) { it.length > 5 };
    println(result);
}

Output

[banana, orange]

Summary

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