Sort characters in NSString into alphabetical order

Question

I\'m trying to re-arrange words into alphabetical order. For example, tomato would become amoott, or stack would become ackst.

I\'ve found some methods to do this in

Answer 1

You could store each of the string's characters into an NSArray of NSNumber objects and then sort that. Seems a bit expensive, so I would perhaps just use qsort() instead.

Here it's provided as an Objective-C category (untested):

NSString+SortExtension.h:

#import 

@interface NSString (SortExtension)
- (NSString *)sorted;
@end

NSString+SortExtension.m:

#import "NSString+SortExtension.h"

@implementation NSString (SortExtension)

- (NSString *)sorted
{
    // init
    NSUInteger length = [self length];
    unichar *chars = (unichar *)malloc(sizeof(unichar) * length);

    // extract
    [self getCharacters:chars range:NSMakeRange(0, length)];

    // sort (for western alphabets only)
    qsort_b(chars, length, sizeof(unichar), ^(const void *l, const void *r) {
        unichar left = *(unichar *)l;
        unichar right = *(unichar *)r;
        return (int)(left - right);
    });

    // recreate
    NSString *sorted = [NSString stringWithCharacters:chars length:length];

    // clean-up
    free(chars);

    return sorted;
}

@end