c# - Regex to remove all special characters from string?

Question

I'm completely incapable of regular expressions, and so I need some help with a problem that I think would best be solved by using regular expressions.

I have list of strings in C#:

List<string> lstNames = new List<string>();
lstNames.add("TRA-94:23");
lstNames.add("TRA-42:101");
lstNames.add("TRA-109:AD");

foreach (string n in lstNames) {
  // logic goes here that somehow uses regex to remove all special characters
  string regExp = "NO_IDEA";
  string tmp = Regex.Replace(n, regExp, "");
}

I need to be able to loop over the list and return each item without any special characters. For example, item one would be "TRA9423", item two would be "TRA42101" and item three would be TRA109AD.

Is there a regular expression that can accomplish this for me?

Also, the list contains more than 4000 items, so I need the search and replace to be efficient and quick if possible.

EDIT: I should have specified that any character beside a-z, A-Z and 0-9 is special in my circumstance.

Answer 1

It really depends on your definition of special characters. I find that a whitelist rather than a blacklist is the best approach in most situations:

tmp = Regex.Replace(n, "[^0-9a-zA-Z]+", "");

You should be careful with your current approach because the following two items will be converted to the same string and will therefore be indistinguishable:

"TRA-12:123"
"TRA-121:23"