sort dictionaries by key's value in an array

sort_dictionary_array.m

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        // insert code here...
        NSLog(@"Hello, World!");
        
        NSArray *arr = [NSArray arrayWithObjects:
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:5], @"a", [NSNumber numberWithInt:5], @"b",nil],
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:6], @"a", [NSNumber numberWithInt:2], @"b",nil],
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:2], @"a", [NSNumber numberWithInt:7], @"b",nil],
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:5], @"a", [NSNumber numberWithInt:2], @"b",nil],
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:1], @"a", [NSNumber numberWithInt:0], @"b",nil],
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:5], @"a", [NSNumber numberWithInt:1], @"b",nil],
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:6], @"a", [NSNumber numberWithInt:1], @"b",nil],
                        [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInt:2], @"a", [NSNumber numberWithInt:9], @"b",nil],
                        nil];
    
        
        
        
        NSSortDescriptor *aDescriptor = [[NSSortDescriptor alloc] initWithKey:@"a" ascending:NO];
        NSSortDescriptor *bDateDescriptor = [[NSSortDescriptor alloc] initWithKey:@"b" ascending:YES];
        NSArray *sortDescriptors = @[aDescriptor, bDateDescriptor];
        NSArray *sortedArray = [arr sortedArrayUsingDescriptors:sortDescriptors];

        NSLog(@"after sort the arr is:%@", sortedArray);
    }
    return 0;
}