NSString+GroupedDelimitedString Category

gistfile1.m

#import <Foundation/Foundation.h>

@interface NSString (GroupedDelimitedString)

- (NSString *)stringByGroupingBySize:(NSInteger)groupSize withDelimiter:(NSString *)delimiter;

@end

gistfile2.m

#import "NSString+GroupedDelimitedString.h"

@implementation NSString (GroupedDelimitedString)

- (NSString *)stringByGroupingBySize:(NSInteger)groupSize withDelimiter:(NSString *)delimiter {
    NSString *stringToGroup = [self stringByReplacingOccurrencesOfString:delimiter withString:@""];
    
    if (stringToGroup.length > groupSize) {
        NSMutableString *paddedString = [NSMutableString string];
        
        for (NSInteger index = 0; index < stringToGroup.length; index++) {
            if (index % groupSize == 0){
                
                if (index + groupSize < stringToGroup.length) {
                    [paddedString appendFormat:@"%@%@", [stringToGroup substringWithRange:NSMakeRange(index, groupSize)], delimiter];
                } else {
                    /* final group */
                    NSInteger finalLength = stringToGroup.length - index;
                    [paddedString appendString:[stringToGroup substringWithRange:NSMakeRange(index, finalLength)]];
                }
            }
        }
        
        return paddedString;
    } else {
        return self;
    }
}

@end