How to strip away letters from string?

Question

I want to strip away all letters in a string, which are not numeric. Preferably a solution made with Regular Expressions or something. And in C#. How to do that?

Answer 1

Using Regex:

str = Regex.Replace(str, @"\D+", "");

\D is the complement of \d - matches everything that isn't a digit. + will match one or more of them (it usually works a little better than one by one).

Using Linq (on .Net 4.0):

str = String.Concat(str.Where(Char.IsDigit));