Myujth

Currently I am using a StringBuilder to remove a list of characters from a string as below

char charArray = ', '<', '>', 
 ';', ':', ',', '"', '(', ')', '[', ']', '\', 
 '/', '*', '+', ' ' ;

// Remove special characters that aren't allowed

var sanitizedAddress = new StringBuilder();
foreach (var character in emailAddress.ToCharArray())

 if (Array.IndexOf(charArray, character) < 0)
 sanitizedAddress.Append(character);

I tried to use Regex for the same as follows

var invalidCharacters = Regex.Escape(@"%&=?|<>;:,"()\/*+s");
emailAddress = Regex.Replace(emailAddress, invalidCharacters, "");

You can try using Linq (in order to filter out the unwanted characters with a help of Where) instead of Regular Expressions:

using System.Linq;

...

// Hash set is faster on Contains operation than array - O(1) vs. O(N)
HashSet<char> toRemove = new HashSet<char>() 
 '%', '&', '=', '?', '', '', ';

string emailAddress = ...

string emailAddress = string.Concat(emailAddress
 .Where(c => !toRemove.Contains(c)));

You can add more Where e.g.

string emailAddress = string.Concat(emailAddress
 .Where(c => !toRemove.Contains(c))
 .Where(c => !char.IsWhiteSpace(c))); // get rid of white spaces as well

In case you insist on regular expressions you have to build the pattern, e.g.:

 char charArray = ', '<', '>',
 ';', ':', ',', '"', '(', ')', '[', ']', '\',
 '/', '*', '+', ' ' ;

 // Joined with | ("or" in regular expressions) all the characters (escaped!)
 string pattern = string.Join("|", charArray
 .Select(c => Regex.Escape(c.ToString())));

And then you can Replace:

 string emailAddress = Regex.Replace(emailAddress, pattern, "");

You can use character set [...] for this:

var invalidCharacters = "[" + Regex.Escape(@"%&=?|<>;:,""()*/+") + @"][s]";
emailAddress = Regex.Replace(emailAddress, invalidCharacters, "");

Some side notes:

• when using double quote in "at string", you should use "", not "
  


• 
  s is alread an escaped sequence, so Regex.Escape will render \s, which is not what you wanted


• 
  Regex.Escape don't seem to escape ] character correctly - that's why it's added separately