Using NSPredicate to filter an NSArray based on NSDictionary keys

Question

I have an array of dictionaries.

I want to filter the array based on a key.

I tried this:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(SPORT ==  %@)", @"Football"];

NSArray *filteredArray = [data filteredArrayUsingPredicate:predicate];

This doesn't work, I get no results. I think I'm doing something wrong. I know this is the method if "SPORT" was an ivar. I think it is probably different if it is a key.

I haven't been able to find an example however.

Thanks

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Update

I added quotes around the string I am searching for.

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(SPORT ==  '%@')", @"Football"];

It still does not work.

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Update 2

Solved it. I actually had to remove the single quotes, which seems to go against what the guide says.

My real problem is I had a nested array and I wasn't actually evaluating the dictionaries. Bone head move.

Answer 1

Looking at the NSPredicate reference, it looks like you need to surround your substitution character with quotes. For example, your current predicate reads: (SPORT == Football) You want it to read (SPORT == 'Football'), so your format string needs to be @"(SPORT == '%@')".

Answer 2

It should work - as long as the data variable is actually an array containing a dictionary with the key SPORT

NSArray *data = [NSArray arrayWithObject:[NSMutableDictionary dictionaryWithObject:@"foo" forKey:@"BAR"]];    
NSArray *filtered = [data filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"(BAR == %@)", @"foo"]];

Filtered in this case contains the dictionary.

(the %@ does not have to be quoted, this is done when NSPredicate creates the object.)

Answer 3

NSPredicate is only available in iPhone 3.0.

You won't notice that until try to run on device.

Answer 4

Just to mention that the predicate is case sensitive by default (use [c] to get unsensitive).