Replace elements in List by condition

Question

I have a pretty much large val s: List[Int] = //..., a function f: Int => Boolean and a function transform: Int => Int.

The problem: I want to create another List[Int] such that all elements e: Int of the s: List[Int] such that f(e) = true are replaced with transform(e).

I looked at cats-mtl FunctorEmpty (to adhere to functional programming style), but it does not seem to work in my case. Maybe some cats/scalaz data structures can be useful here? Or any other way?

Possible duplicate of: https://stackoverflow.com/questions/33788185/find-and-replace-item-in-scala-collection — Sid, Jun 23 '18 at 13:47
If you don't want transform then you want to keep same or you want to remove it? — Manoj Kumar Dhakad, Jun 23 '18 at 13:48

Andrey Tyukin · Accepted Answer · 2018-06-23T14:09:10.697

6

s.map{ e => if(f(e)) transform(e) else e }

edited Jun 23 '18 at 14:09

answered Jun 23 '18 at 13:47

Andrey Tyukin

43,673
4
57
93

1

Oh... you are exactly right. Thanks. I thought of much more complicated cats-based solution. Damn :( – St.Antario Jun 23 '18 at 13:49

score 0 · Answer 2 · answered Jun 29 '18 at 12:58

List(1, 2, 3).map(fn) creates a new list which might be not exactly want you need, especially if input is large.

Alternative solution would be to map on view List(1, 2, 3).view.map(...) without creating a new list and only "materialize" results when you need them

Replace elements in List by condition

2 Answers2

Linked