Strip Non-Alphanumeric Characters from an NSString

We can do this by splitting and then joining. Requires OS X 10.5+ for the componentsSeparatedByCharactersInSet:

NSCharacterSet *charactersToRemove = [[NSCharacterSet alphanumericCharacterSet] invertedSet];
NSString *strippedReplacement = [[someString componentsSeparatedByCharactersInSet:charactersToRemove] componentsJoinedByString:@""];