String with allowed chars - iphone

Question

Is there a clean way to get a string containing only allowed characters?
for example:
NSString* myStr = #"a5&/Öñ33";
NSString* allowedChars = #"abcdefghijklmnopqrstuvwxyz0123456789";
NSString* result = [myStr stringWIthAllowedChrs:allowedChars];
result should now be #"a533";

Answer 1

It's not the cleanest, but you could separate the string using a character set, and then combine the resulting array using an empty string.
// Create a character set with every character not in allowedChars
NSCharacterSet *charSet = [[NSCharacterSet characterSetWithCharactersInString:allowedChars] invertedSet];
// Split the original string at any occurrence of those characters
NSArray *splitString = [myStr componentsSeparatedByCharactersInSet:charSet];
// Combine the result into a string
NSString *result = [splitString componentsJoinedByString:#""];

Answer 2

Simple and easy to customize and understand approach:
NSString* myStr = #"a5&/Öñ33";
NSString* allowedChars = #"abcdefghijklmnopqrstuvwxyz0123456789";
NSCharacterSet *set = [[NSCharacterSet characterSetWithCharactersInString:allowedChars] invertedSet];
NSString *result = myStr;
NSRange range = [result rangeOfCharacterFromSet:set];
while (range.location != NSNotFound)
{
result = [result stringByReplacingCharactersInRange:range withString:#""];
range = [result rangeOfCharacterFromSet:set];
}
NSLog(#"%#", result);

Answer 3

One of the simplest-
NSString* result = #"";
for(NSUInteger i = 0; i < [myStr length]; i++)
{
unichar charArr[1] = {[myStr characterAtIndex:i]};
NSString* charString = [NSString stringWithCharacters:charArr length:1];
if([allowedChars rangeOfString:charString].location != NSNotFound)
result = [result stringByAppendingString:charString];
}
return result;