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

Question

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 which has [theObject.type isEqualToString:@"standard"].

I remember that it was possible to use predicates somehow for this kind of stuff, right?

Gocart

Answer 1

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"type == %@", @"standard"];
NSArray *filteredArray = [myArray filteredArrayUsingPredicate:predicate];
id firstFoundObject = nil;
firstFoundObject =  filteredArray.count > 0 ? filteredArray.firstObject : nil;

NB: The notion of the first found object in an NSSet makes no sense since the order of the objects in a set is undefined.

Milda

Does it work if the object doesn't have the 'type' property, but has another object (let's say 'job'), and this is 'job' which has the 'type' property? – Zinc

Yes, but a class must be key-value coding compliant for the keys you want to use in a predicate. – Therapsid

indexOfObjectPassingTest seems better for two reasons: (1) You use an actual method rather than a string (2) You stop on the "first" element you find - it doesn't matter that a set is not ordered, you may still want just one item. – Sandisandidge

Answer 2

You can get the filtered array as Jason and Ole have described, but since you just want one object, I'd use - indexOfObjectPassingTest: (if it's in an array) or -objectPassingTest: (if it's in a set) and avoid creating the second array.

Hundred

That seems a good idea for an NSArray, but the method in NSSet is actually -objectsPassingTest: (note the plural), so this idea isn't directly possible there, if I understand this correctly. – Pubis

Answer 3

Generally, I use indexOfObjectPassingTest: as I find it more convenient to express my test in Objective-C code rather than NSPredicate syntax. Here's a simple example (imagine that integerValue was actually a property):

NSArray *array = @[@0,@1,@2,@3];
NSUInteger indexOfTwo = [array indexOfObjectPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
    return ([(NSNumber *)obj integerValue] == 2);
}];
NSUInteger indexOfFour = [array indexOfObjectPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
    return ([(NSNumber *)obj integerValue] == 4);
}];
BOOL hasTwo = (indexOfTwo != NSNotFound);
BOOL hasFour = (indexOfFour != NSNotFound);
NSLog(@"hasTwo: %@ (index was %d)", hasTwo ? @"YES" : @"NO", indexOfTwo);
NSLog(@"hasFour: %@ (index was %d)", hasFour ? @"YES" : @"NO", indexOfFour);

The output of this code is:

hasTwo: YES (index was 2)
hasFour: NO (index was 2147483647)

Handball

Answer 4

NSArray* results = [theFullArray filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF.type LIKE[cd] %@", @"standard"]];

Formative