How to split a list by another list in Scala

Question

I am new to Scala and I need a solution to my problem. Imagine I have these lists:

val list1 = List(1,2,3,4,5,6,7,8,9,10,11)
val list2 = List(6,5)
         


        

Answer 1

You can use a combination of scanLeft and splitAt:

list2.scanLeft((List.empty[Int], list1)) { 
  case ((_, remaining), i) =>  remaining.splitAt(i)
}.unzip._1.tail

Gives:

List(List(1, 2, 3, 4, 5, 6), List(7, 8, 9, 10, 11))

Brief explanation: each step of scanLeft saves each piece of list1 and the remaining elements of list1 in a tuple. The remaining elements are split according to the size i of next chunk, where i is an element of list2. In the end, all the "remainders" are thrown away by unzip._1, and the first empty dummy-element is removed by tail.

Note that since the list structure is immutable & persistent, the intermediate results stored in the second component of the tuple in each step do not take up any extra space, they are mere references to tails of list1.