Kotlin List union()
Syntax & Examples

Syntax of List.union()

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

infix fun <T> Iterable<T>.union(other: Iterable<T>): Set<T>

This union() extension function of List returns a set containing all distinct elements from both collections.

✐ Examples

1 Example

In this example,

We create a list named list1 containing the integers 1, 2, 3, 4, 5.
We create another list named list2 containing the integers 4, 5, 6, 7, 8.
We perform the union operation on list1 and list2 using the union() extension function, which returns a set containing all distinct elements from both lists.
We print the elements of the resulting set resultSet joined into a string to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(1, 2, 3, 4, 5)
    val list2 = listOf(4, 5, 6, 7, 8)
    val resultSet = list1.union(list2)
    println(resultSet.joinToString())
}

Output

1, 2, 3, 4, 5, 6, 7, 8

2 Example

In this example,

We create a list named list1 containing characters 'a', 'b', 'c', 'd'.
We create another list named list2 containing characters 'd', 'e', 'f'.
We perform the union operation on list1 and list2 using the union() extension function, which returns a set containing all distinct characters from both lists.
We print the elements of the resulting set resultSet joined into a string to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf('a', 'b', 'c', 'd')
    val list2 = listOf('d', 'e', 'f')
    val resultSet = list1.union(list2)
    println(resultSet.joinToString())
}

Output

a, b, c, d, e, f

3 Example

In this example,

We create a list named list1 containing strings "apple", "banana", "cherry".
We create another list named list2 containing strings "banana", "orange", "pear".
We perform the union operation on list1 and list2 using the union() extension function, which returns a set containing all distinct strings from both lists.
We print the elements of the resulting set resultSet joined into a string to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("apple", "banana", "cherry")
    val list2 = listOf("banana", "orange", "pear")
    val resultSet = list1.union(list2)
    println(resultSet.joinToString())
}

Output

apple, banana, cherry, orange, pear

Summary

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