Sorting array of custom objects using the value of an internal object's instance variable

Question

(sorry about the long title)

I have a custom object Person, which in turn has an NSSet which has several custom objects called Appointment. A Person therefo

Answer 1

You can use sort descriptors and KVC collection operators:

NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"appointments.@min.startSecond" ascending:YES];

For example, in a CoreData fetch:

NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:@"Person"];

NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"appointments.@min.startSecond" ascending:YES];
[request setSortDescriptors:@[sortDescriptor]];

NSError *error = nil;
NSArray *sortedResults = [context executeFetchRequest:request error:&error];

Or just sorting an array:

NSArray *people = @[...];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"appointments.@min.startSecond" ascending:YES];

NSArray *sortedPeople = [people sortedArrayUsingDescriptors:@[sortDescriptor]];

More information on KVC collection operators can be found in the KVC Programming Guide.

Answer 2

A suggestion:

// Sorting key
NSString *key = @"startSecond";

// A mutable array version of your list of Persons.
NSMutableArray *a = [NSMutableArray arrayWithObjects:Person1, Person2, Person3, nil];

// Then use the sorted appointements to get your sorted person array.
[a sortUsingComparator:^NSComparisonResult(Person *p1, Person *p2) {
    NSSortDescriptor *sortDesc1 = [NSSortDescriptor sortDescriptorWithKey:key ascending:NO];
    NSArray *sortedApp1 = [p1.appointements sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDesc1]];

    NSSortDescriptor *sortDesc2 = [NSSortDescriptor sortDescriptorWithKey:key ascending:NO];
    NSArray *sortedApp2 = [p2.appointements sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDesc2]];

    return [[[sortedApp1 objectAtIndex:0] valueForKey:key] compare:[[sortedApp2 objectAtIndex:0] valueForKey:key]];
}

Answer 3

If you have the data in an NSArray form you can sort it like this:

NSArray *sortedPersonArray = [coreDataPersonArray sortedArrayUsingSelector:@selector(compare:)];

- (NSComparisonResult)compare:(Person *)personObject {
    return [self.startSecond compare:personObject.startSecond];
}