How can I efficiently trim selected characters from middle of a string?

Can anyone think of an efficient way (time wise) to trim a few selected characters from the middle of a string?

Best I came up with was:

public static string Trim(this string word, IEnumerable<char> selectedChars)
{
    string result = word;
    foreach (char c in selectedChars)
        result = result.Replace(c.ToString(), "");
    return result;
}

But it is still too slow.

From stackoverflow

• Two options spring to mind:

  • Use a StringBuilder
  • Use a regular expression

  Here's the StringBuilder version:

  public static string Trim(this string word, IEnumerable<char> selectedChars)
  {
      // The best form for this will depend largely on the size of selectedChars
      // If you can change how you call the method, there are optimisations you
      // could do here
      HashSet<char> charSet = new HashSet<char>(selectedChars);
  
      // Give enough capacity for the whole word. Could be too much,
      // but definitely won't be too little
      StringBuilder builder = new StringBuilder(word.Length);
  
      foreach (char c in word)
      {
          if (!charSet.Contains(c))
          {
              builder.Append(c);
          }
      }
      return builder.ToString();
  }
  

  The regular expression option could be very efficient if you have a fixed set of chars you want to trim, and can build the regex once.

  Something like:

  // Put this statically somewhere
  Regex unwantedChars = new Regex("[def]", RegexOptions.Compiled);
  
  // Then do this every time you need to use it:
  word = unwantedChars.Replace(word, "");
  

• start by using StringBuilder not string for your replacements...
  see http://blogs.msdn.com/charlie/archive/2006/10/11/Optimizing-C_2300_-String-Performance.aspx