您可能必须亲自编写此过滤方法:

You might have to actually write this filtering method yourself:

@interface NSArray (CustomFiltering)
@end

@implementation NSArray (CustomFiltering) 

- (NSArray *) filterObjectsByKey:(NSString *) key {
   NSMutableSet *tempValues = [[NSMutableSet alloc] init];
   NSMutableArray *ret = [NSMutableArray array];
   for(id obj in self) {
       if(! [tempValues containsObject:[obj valueForKey:key]]) {
            [tempValues addObject:[obj valueForKey:key]];
            [ret addObject:obj];
       }
   }
   [tempValues release];
   return ret;
}

@end