Extract numbers from string to create digit only string

You could write a simple method to extract out all non-digit characters, though this won't handle floating point data:

public string ExtractNumber(string original)
{
     return new string(original.Where(c => Char.IsDigit(c)).ToArray());
}

This purely pulls out the "digits" - you could also use Char.IsNumber instead of Char.IsDigit, depending on the result you wish.

Try this oneliner:

Regex.Replace(str, "[^0-9 _]", "");