how to modify items in a Generic List using foreach?

c# foreach generic-list
Anthony picture Anthony · Jun 7, 2009 · Viewed 7.2k times · Source

I have the following Generic List which is populated with a list of string: 

List<string> mylist =new List<string>();  
myList.add("string1");  
myList.add("string2");

Say I want to add 'test' at the end of each string, how can I do it in a simple way? Intuitively, I tried this which compiles ok: 

myList.ForEach(s => s = s + "test");

But if I then look at the content of the List, nothing has changed. I guess I could use a for loop to iterate through the List but I'm looking for something very simple and using ForEach looks very neat.... but doesn't seem to work. Any ideas?

Answer

jerryjvl picture jerryjvl · Jun 7, 2009

The problem is that the Action you specified gets executed on the elements of the list, but the result is not put back anywhere... your s is a local variable only.

Changing the list in-place will probably take an actual foreach, but if you are happy to take a new list as the result, you could try:

list = list.ConvertAll(s => s + "test");

Not quite the same... but as close as you'll get...

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