Filtering an NSArray with custom objects

Question

I have a class like this :

@interface MyObject : NSObject 
@property (nonatomic, strong) NSString *type;
@end

and I am creating an array like this:

NSMutableArray *array = [NSMutableArray array];
MyObject *obj = [[MyObject alloc] init];
obj.type = @"test1";
[array addObject:obj];

MyObject *obj2 = [[MyObject alloc] init];
obj2.type = @"test2";
[array addObject:obj2];

MyObject *obj3 = [[MyObject alloc] init];
obj3.type = @"test1";
[array addObject:obj3];

I would like to filter the array to just have only the objects which have different types, in my example just to have obj1, obj2 and remove the obj3.

If you don't mind efficiency, just use a nested loop to remove objects appearing a second time, and then sort (sorting has little to do with removing objects having the same types however). — Khanh Nguyen, Jul 04 '13 at 14:14
Sorry for the closing vote. I've read your question quicly. Cheers. — Lorenzo B, Jul 04 '13 at 14:15
If any moderator can remove the closing vote, this would help. Thanks — Lorenzo B, Jul 04 '13 at 14:18

score 4 · Accepted Answer · answered Jul 04 '13 at 14:19

Something along these lines should do the trick:

NSMutableSet * types = [NSMutableSet setWithCapacity:10];
NSPredicate * filterPredicate = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {

    if ([types containsObject:[evaluatedObject type]]) {
        return NO;
    }
    else {
        [types addObject:[evaluatedObject type]];
        return YES
    }
}];
NSArray * filteredArray = [detailedError filteredArrayUsingPredicate:filterPredicate];

The above code keeps the first object of each type and removes others.

Ramy Al Zuhouri · Answer 2 · 2013-07-04T14:42:42.850

2

I would do this by just overriding hash and isEqual:

- (BOOL) isEqual:(id)object
{
    if([object isKindOfClass: [self class]])
        return [_type isEqualToString: object];
    return NO;
}

- (NSInteger) hash
{
    return [_type hash];
}

Then taking the distinct objects array from a set created from the array:

NSArray* filteredArray= [NSSet setWithArray: array].allObjects;

edited Jul 04 '13 at 14:42

answered Jul 04 '13 at 14:28

Ramy Al Zuhouri

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Even though this is very elegant solution for this problem, I think it might have side effects if the OP needs to use isEqual: somewhere else, maybe obj1.type == obj2.type does not always necessitate obj1==obj2 – Engin Kurutepe Jul 04 '13 at 14:56
This is intended to be used on a class like OP's *MyObject*, which has only *type* and no other properties. – Ramy Al Zuhouri Jul 04 '13 at 15:04

Filtering an NSArray with custom objects

2 Answers2