objective c - NSPredicate on array of arrays

Question

I have an array, that when printed out looks like this:

(
        (
        databaseVersion,
        13
    ),
        (
        lockedSetId,
        100
    )
)

Would it be possible to filter this using an NSPredicate (potentially by the index in the array). So something like: give me all rows where element 0 is 'databaseVersion'? I know that if I had an array of dictionaries I could do this with a predicate similar the one found here, but I found that when using dictionaries and storing a large amount of data, my memory consumption went up (from ~80mb to ~120mb), so if possible I would to keep the array. Any suggestions on how this might be done?

Answer 1

This can be done using "SELF[index]" in the predicate:

NSArray *array = @[
    @[@"databaseVersion", @13],
    @[@"lockedSetId", @100],
    @[@"databaseVersion", @55],
    @[@"foo", @"bar"]
];

NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF[0] == %@", @"databaseVersion"];
NSArray *filtered = [array filteredArrayUsingPredicate:pred];
NSLog(@"%@", filtered);

Output:

(
        (
        databaseVersion,
        13
    ),
        (
        databaseVersion,
        55
    )
)

Or you can use a block-based predicate:

NSPredicate *pred = [NSPredicate predicateWithBlock:^BOOL(NSArray *elem, NSDictionary *bindings) {
    return [elem[0] isEqualTo:@"databaseVersion"];
}];