Divide list into parts

Question

Is there a simple way to divide list into parts (maybe some lambda) in Kotlin?

For example:

[1, 2, 3, 4, 5, 6] => [[1, 2], [3, 4], [5, 6]] 

Answer 1

Since Kotlin 1.2 you can use Iterable<T>.chunked(size: Int): List<List<T>> function from stdlib (https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/chunked.html).

Answer 2

Given the list: val list = listOf(1, 2, 3, 4, 5, 6) you can use groupBy:

list.groupBy { (it + 1) / 2 }.map { it.value } 

Or if your values are not numbers you can first assign an index to them:

list.withIndex()     .groupBy { it.index / 2 }     .map { it.value.map { it.value } } 

Or if you'd like to save some allocations you can go a bit more manual way with foldIndexed:

list.foldIndexed(ArrayList<ArrayList<Int>>(list.size / 2)) { index, acc, item ->     if (index % 2 == 0) {         acc.add(ArrayList(2))     }     acc.last().add(item)     acc }