Memory Efficiency and Performance of String.Replace .NET Framework

All characters in a .NET string are “unicode chars”. Do you mean they’re non-ascii? That shouldn’t make any odds – unless you run into composition issues, e.g. an “e + acute accent” not being replaced when you try to replace an “e acute”.

You could try using a regular expression with Regex.Replace, or StringBuilder.Replace. Here’s sample code doing the same thing with both:

using System;
using System.Text;
using System.Text.RegularExpressions;

class Test
{
    static void Main(string[] args)
    {
        string original = "abcdefghijkl";

        Regex regex = new Regex("a|c|e|g|i|k", RegexOptions.Compiled);

        string removedByRegex = regex.Replace(original, "");
        string removedByStringBuilder = new StringBuilder(original)
            .Replace("a", "")
            .Replace("c", "")
            .Replace("e", "")
            .Replace("g", "")
            .Replace("i", "")
            .Replace("k", "")
            .ToString();

        Console.WriteLine(removedByRegex);
        Console.WriteLine(removedByStringBuilder);
    }
}

I wouldn’t like to guess which is more efficient – you’d have to benchmark with your specific application. The regex way may be able to do it all in one pass, but that pass will be relatively CPU-intensive compared with each of the many replaces in StringBuilder.