What is the Kotlin equivalent for Dart's List.expand() method?

Question

In Dart, List.expand() allows mapping each element of the existing List into zero, one, or multiple elements, and then assemble them as a new Iterable. Such as,

var a=[1,2,3];
var b = a.expand((i)=>List.generate(i,(_)=>i.toString())).toList();
print(b.toString());
//Output: [1, 2, 2, 3, 3, 3]

Basically an enhanced map() function allows "one to many" mapping

What is the Kotlin equivalent if I want to do the same? I failed to find corresponding method in Kotlin collections.

user_750510 · Answer

Use flatMap:

fun main(args: Array) {
    val a = listOf(0, 1, 2, 3) // listOf(1, 2, 3)
    val b = a.flatMap({i ->
        List(i) { i }
    })

    println(b)
}

> [1, 2, 2, 3, 3, 3]

List(i) { i } is a cool comprehension for your list generator. Play online with this code on https://try.kotlinlang.org!

What is the Kotlin equivalent for Dart's List.expand() method?

1 Answers