arrTripCat :
(
    { tripcategory = "general_tourism"; },
    { tripcategory = nightlife; },
    { tripcategory = "art_museums"; },
    { tripcategory = nightlife; },
    { tripcategory = architecture; },
    { tripcategory = nightlife; }
);

NSArray *arrTripCat = [NSArray arrayWithArray:[self.dictSearchResult objectForKey:@"TripCategories"]];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY SELF.@allKeys contains[cd] %@",@"tripcategory"];

NSMutableArray *filteredArray = [[NSMutableArray alloc] init];
[filteredArray addObjectsFromArray:[arrTripCat filteredArrayUsingPredicate:predicate]];

filteredArray:
(
    { tripcategory = "general_tourism"; },
    { tripcategory = nightlife; },
    { tripcategory = "art_museums"; },
    { tripcategory = nightlife; },
    { tripcategory = architecture; },
    { tripcategory = nightlife; }
);

( general_tourism, nightlife, art_museums, architecture )

NSArray *tripCategories = [arrTripCat valueForKey:@"tripcategory"];

NSMutableArray *results = @[].mutableCopy;
for (NSDictionary *dict in arrTripCat) {
   [results addObject:dict[@"tripcategory"];
}