Kotlin List filterNotNullTo()
Syntax & Examples

Syntax of List.filterNotNullTo()

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

fun <C : MutableCollection<in T>, T : Any> Iterable<T?>.filterNotNullTo( destination: C ): C

This filterNotNullTo() extension function of List appends all elements that are not null to the given destination.

✐ Examples

1 Example

In this example,

We create a list named list1 containing integers and null values.
We create an empty mutable list named result to store the non-null elements.
We use the filterNotNullTo function on list1 to filter out null elements and append non-null elements to result.
Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(1, null, 3, null, 5)
    val result = mutableListOf<Int>()
    list1.filterNotNullTo(result)
    println(result)
}

Output

[1, 3, 5]

2 Example

In this example,

We create a list named list2 containing strings and null values.
We create an empty mutable list named result to store the non-null strings.
We use the filterNotNullTo function on list2 to filter out null elements and append non-null strings to result.
Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list2 = listOf("apple", null, "cherry", "date")
    val result = mutableListOf<String>()
    list2.filterNotNullTo(result)
    println(result)
}

Output

[apple, cherry, date]

3 Example

In this example,

We create a list named list3 containing characters and null values.
We create an empty mutable list named result to store the non-null characters.
We use the filterNotNullTo function on list3 to filter out null elements and append non-null characters to result.
Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list3 = listOf('a', null, 'c', null, 'e')
    val result = mutableListOf<Char>()
    list3.filterNotNullTo(result)
    println(result)
}

Output

[a, c, e]

Summary

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