iPhone – getting unique values from NSArray object

Take a look at keypaths. They are super powerful and I use them instead of NSPredicate classes most of the time. Here is how you would use them in your example…

NSArray *uniqueStates;
uniqueStates = [customObjects valueForKeyPath:@"@distinctUnionOfObjects.state"];

Note the use of valueForKeyPath instead of valueForKey.

Here is a more detailed/contrived example…

NSDictionary *arnold = [NSDictionary dictionaryWithObjectsAndKeys:@"arnold", @"name", @"california", @"state", nil];
NSDictionary *jimmy = [NSDictionary dictionaryWithObjectsAndKeys:@"jimmy", @"name", @"new york", @"state", nil];
NSDictionary *henry = [NSDictionary dictionaryWithObjectsAndKeys:@"henry", @"name", @"michigan", @"state", nil];
NSDictionary *woz = [NSDictionary dictionaryWithObjectsAndKeys:@"woz", @"name", @"california", @"state", nil];

NSArray *people = [NSArray arrayWithObjects:arnold, jimmy, henry, woz, nil];

NSLog(@"Unique States:\n %@", [people valueForKeyPath:@"@distinctUnionOfObjects.state"]);

// OUTPUT
// Unique States:
// "california",
// "michigan",
// "new york"