如何将NSArray的字符串转换为一个唯一字符串数组,顺序相同？

NSArray *array = @[@"apple", @"banana", @"orange", @"grape"];
NSString *uniqueString = [array.firstObject stringByAppendingString:@" "]
                                     withFormat:@"%@,%@", [array.firstObject stringByAppendingString:@" "]
                                     withFormat:@"%@,%@", ...];

NSArray *array = @[@"apple", @"banana", @"orange", @"grape"];
NSString *uniqueString = [array.firstObject stringByAppendingString:@" "]
                                     withFormat:@"%@", [array.firstObject stringByAppendingString:@" "]
                                     withFormat:@"%@", ...];

NSArray *array = @[@"apple", @"banana", @"orange", @"grape"];
NSString *uniqueString = [array sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    return [obj1 compare:obj2];
}]
               componentsJoinedByString:@","];