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"))

In a single statement this would do the work: metricList = metricList.ConvertAll(s => s.Replace("XX", "1")); — Scordo
– Scordo, Commented Mar 12, 2014 at 11:06

Dan Puzey · Accepted Answer · 2014-03-12 11:13:56Z

49

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();

edited Mar 12, 2014 at 11:13

answered Mar 12, 2014 at 11:09

Dan Puzey

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2 Comments

Scordo Over a year ago

Since he stated that he's using a generic list I would suggest ConvertAll(), because it does not iterate twice over the collection like Select & ToList together.

Bob Vale Over a year ago

Select doesnt iterate the list it just defines and enumerable that the two list iterates over. One iteration

Max · Accepted Answer · 2014-03-12 11:21:07Z

16

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

edited Mar 12, 2014 at 11:21

answered Mar 12, 2014 at 11:07

Max

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1 Comment

Scordo Over a year ago

The "ForEach" in your Linq version should be a "Select"

Leniel Maccaferri · Accepted Answer · 2020-12-02 22:41:42Z

1

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

edited Dec 2, 2020 at 22:41

Leniel Maccaferri

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answered Mar 12, 2014 at 11:02

Regfor

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2 Comments

Max Over a year ago

You notice the cause here, but don't offer an option that solves it.

Regfor Over a year ago

It is the option. You need to assign result of String.Replace method and use select means in code - .Select(x => x.Replace("a","b"))

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