NSArray *aryFName = @[ @"Alice", @"Bob", @"Charlie", @"Quentin" ];
NSArray *aryLName = @[ @"Smith", @"Jones", @"Smith", @"Alberts" ];
NSArray *aryAge = @[ @24, @27, @33, @31 ];
    
//Create a Custom class with properties for firstName & lastName of type NSString *,
//and age, which is an NSUInteger.
    
NSMutableArray *aryPerson = [NSMutableArray array];
[firstNames enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    Person *person = [[Person alloc] init];
    person.firstName = [aryFName objectAtIndex:idx];
    person.lastName = [aryLName objectAtIndex:idx];
    person.age = [aryAge objectAtIndex:idx];
    [aryPerson addObject:person];
}];
    
NSSortDescriptor *firstNameSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"firstName"
                                             ascending:YES
                                             selector:@selector(localizedStandardCompare:)];

NSSortDescriptor *lastNameSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"lastName"
                                            ascending:YES
                                            selector:@selector(localizedStandardCompare:)];

NSSortDescriptor *ageSortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"age"
                                       ascending:NO];
    
NSLog(@"By age: %@", [aryPerson sortedArrayUsingDescriptors:@[ageSortDescriptor]]);
// "Charlie Smith", "Quentin Alberts", "Bob Jones", "Alice Smith"
    
    
NSLog(@"By first name: %@", [aryPerson sortedArrayUsingDescriptors:@[firstNameSortDescriptor]]);
// "Alice Smith", "Bob Jones", "Charlie Smith", "Quentin Alberts"
    
    
NSLog(@"By last name, first name: %@", [aryPerson sortedArrayUsingDescriptors:@[lastNameSortDescriptor, firstNameSortDescriptor]]);
// "Quentin Alberts", "Bob Jones", "Alice Smith", "Charlie Smith"