Useful method for grouping items in an array

gistfile1.m

@implementation NSArray (FunctionalKit)

- (NSDictionary *)collectWithBlock:(id (^)(id value)) valueIdentifier {
   NSMutableDictionary *dict = [NSMutableDictionary new];
   
   for (id object in self) {
      id ident = valueIdentifier(object);
      NSMutableArray *array = [dict objectForKey:ident];
      
      if (!array) {
         array = [NSMutableArray new];
         [dict setValue:array forKey:ident];
      }
      
      [array addObject:object];
   }
   
   return [NSDictionary dictionaryWithDictionary:dict];
}
@end