字串只留下數字，或只留下文字

using System.Text.RegularExpressions;

string  inputStr = "abc123";

 var outputNum = Regex.Replace( inputStr, @"[\D-]", string.Empty); //只有數字被保留

 var outputStr = Regex.Replace( inputStr, @"[\d-]", string.Empty); //只有文字被保留