Replace string values in list

Question

I have a collection of strings which contain values like "goalXXvalue,goalXXLength,TestXX". It is a List(of String) I thought I would be able to loop through each item and replace the XX value which I've tried with the method below but the values don't change. Where am I going wrong? Thanks

metricList.ForEach(Function(n) n.Replace("XX", "1"))

Answer 1

Problem: You aren't doing anything with the Replaced strings.
You could easily do this, using a simple loop:

C#

for(int i = 0; i < metricList.Count; i++)
{
    metricList[i] = metricList[i].Replace("XX", "1");
}

VB.NET

For i As Integer = 0 To metricList.Count - 1
    metricList(i) = metricList(i).Replace("XX", "1")
Next

Code iterates through all strings in metricList and replaces XX for 1, it then stores the values back at the correct place in the list, what you aren't doing in your code...

Or using Linq:

C#

var newList = metricList.Select(x => x.Replace("XX", "1")).ToList();

VB.NET

Dim newList = metricList.Select(Function(x) x.Replace("XX", "1")).ToList()

Don't forget to add a reference to linq at the top of your class:

C#

using System.Linq;

VB.NET

Imports System.Linq

Answer 2

You have a few issues here:

• first, strings are immutable, so when you call .Replace you return a new string. Calling n.Replace doesn't modify n.
• assigning to n in your anonymous function won't affect the value that's in your list.
• regardless of the above, you can't change the content of your collection while enumerating it, because it'll invalidate the enumeration.

Since it seems you're changing every string in your list, it seems unnecessary to try to modify the collection in-place. Therefore, the succint solution would be to use Linq would to create a new list:

var newList = metricList.Select(s => s.Replace("XX", "1")).ToList();

Answer 3

You need to assign result of String.Replace method. So your func should return somthing or use instead of foreach select