iPhone - getting unique values from NSArray object

iphone nsarray nspredicate
lostInTransit picture lostInTransit · Sep 17, 2009 · Viewed 39.6k times · Source

I have an NSArray formed with objects of a custom class. The class has 3 (city, state, zip) string properties. I would like to get all unique state values from the array.

I did read through the NSPredicate class but couldn't make much of how to use it in this case. The only examples I could find were for string operations.

Can someone please help me out?

Answer

probablyCorey picture probablyCorey · Sep 17, 2009

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"

Related questions

How to search an NSSet or NSArray for an object which has an specific value for an specific property?

How to search an NSSet or NSArray for an object which has an specific value for an specific property? Example: I have an NSSet with 20 objects, and every object has an type property. I want to get the first object …

Read More
Filter Array with dictionaries using NSPredicate

There is an Array with each element being a NSDictionary. NSMutableArray *mutArr = [NSMutableArray array]; for (Person *person in persons) { NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys:person.name, @"name", person.email, @"email", nil]; [mutArr addObject:dict]; } self.arr = [[NSArray alloc] initWithArray:mutArr]; …

Read More
Filtering NSArray of NSDictionary objects using NSPredicate

I have an NSArray of NSDictionary objects. I want to filter the array based on keys of the dictionaries using NSPredicate. I have been doing something like this: NSString *predicateString = [NSString stringWithFormat:@"%@ == '%@'", key, value]; NSPredicate *predicate = [NSPredicate predicateWithFormat:…

Read More