Linq String Replace

Question

var arr = new[] {"A ", "B ", "C "}.ToList();
        arr.ForEach(a => a = a.Replace(" ", ""));

Why this does not remove space characters from the strings in the array?

This works arr = arr.Select(a => a.Replace(" ", "")).ToList();

ForEach does not modify the original collection, it only uses it as a source of inputs, your code is only updating the local variable to be without spaces, but those new values are not put back into the array. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Mar 30, 2020 at 9:45
@DavidG Duh, sorry, I misread your code and mixed it up with the OPs proposal; arr = arr.Select(a => a.Replace(" ", "")) which is hideous. Sorry about that, you are not mutating anything, simply doing a projection and reassigning arr which is the right apporach. — InBetween
– InBetween, Commented Mar 30, 2020 at 10:01
The only thing about LINQ in your question is the .ToList(). The .ForEach method is just a method on List<>. — Enigmativity
– Enigmativity, Commented Mar 30, 2020 at 10:39

Hans Keﬆing · Accepted Answer · 2020-03-30 10:05:11Z

1

The problem is that a.Replace(..) returns a (reference to) a new string. You do assign that new reference back to the local parameter a. However, that parameter a is a copy of the reference in the list. Updating a does not update the reference in the list itself.

If you want to update "in place", you will have to do it the old fashioned way:

for (var i=0; i<arr.Count; i++)
{
    arr[i] = arr[i].Replace(" ", "");
}

edited Mar 30, 2020 at 10:05

answered Mar 30, 2020 at 10:00

Hans Keﬆing

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