Combine Subtract and Filter in Scala

Question

I am trying to write a function in Scala which takes two integer lists xs and ys and does the following:

• subtracts element by element ys from xs. An example: List(1,2,4) and List(3,2,1) gets you List(-2, 0, 3)

• filters out all elements less than or equal to 0 from the list resulting from step 1.

I am trying to do this using the list functions from the Scala Standard Library

object Solution {
  def combineSubAndFilter(xs: List[Int], ys: List[Int]) = ???
}

Answer 1

The answer, as suggested in the comments by @Luis is:

def combineSubAndFilter(xs: List[Int], ys: List[Int]) = xs.zipAll(ys, 0, 0).collect { case (x,y) if (x > y) => x-y }

From zipAll documentation:

Returns a $coll formed from this $coll and another iterable collection by combining corresponding elements in pairs. If one of the two collections is shorter than the other, placeholder elements are used to extend the shorter collection to the length of the longer.

Code run can be found at Scastie.