Performance & Remove multiple characters from a string in C#

Question

Which is the most performance efficient way to remove multiple characters from a C# string? I have to remove all the spaces, hyphen from a C# string.

Thanks

Answer 1

If you care about performance because the string can be quite large and/or the list of remove-characters is long you should use a StringBuilder.

StringBuilder sb = new StringBuilder(text.Length);
HashSet<Char> removeChars = new HashSet<Char>{ ' ', '-' };
foreach(Char c in text)
{
    if(!removeChars.Contains(c))
        sb.Append(c);
}
text = sb.ToString();

in most cases this should be sufficient:

foreach (String c in new[] { " ", "-" })
    text = text.Replace(c, "");

Answer 2

If the list of characters to remove is large (say more than 10 characters or so, but you'd have to do careful timing to check) then Tim's approach using a HashSet is likely to be the fastest.

However if the list of characters to remove is small, this code might be faster:

public static class StringExt
{
    public static string Remove(this string self, params char[] charsToRemove)
    {
        var result = new StringBuilder();

        foreach (char c in self)
            if (Array.IndexOf(charsToRemove, c) == -1)
                result.Append(c);

        return result.ToString();
    }
}

For your example (removing spaces and hyphen from a string) you could do the following (this removes tabs and newlines too, but just remove those parameters if you don't need them):

string original = "1 2\n3\t4-5";
string result = original.Remove(' ', '-', '\n', '\t');

Answer 3

var input = @"-a b c-";

var index = 0;
var tmp = new char[input.Length];
foreach (var c in input)
{
    if (c != ' ' && c != '-')
    {
        tmp[index++] = c;
    }
}

var result = new string(tmp, 0, index);