Sorting array of dictionaries based on NSNumber

Question

I have array of dictionaries that have NSNumber for key @"id". I want to sort this array based on @"id" value. How can I do it?

Answer 1

You can do this easily with -[NSArray sortedArrayUsingComparator:] and a comparison block.

The comparison block needs to return NSComparisonResult. Fortunately, your values associated with key "id" are NSNumbers, so simply return the result of -[NSNumber compare:].

// Example array containing three dictionaries with "id" keys
NSArray *unsortedArray = @[@{ @"id": @3 },  @{ @"id": @1 }, @{ @"id": @2 }];

NSArray *sortedArray = [unsortedArray sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    return [obj1[@"id"] compare:obj2[@"id"]];
}];

Answer 2

You can sorting dictionary using NSSortDescriptor. Please try this :

  // Example array containing three dictionaries with "id" and "name" keys
  NSArray *unsortedArray = @[@{ @"id":@3, @"name":@"abc"}, @{ @"id":@1, @"name":@"123" }, @{ @"id": @2, @"name":@"xyz" }];
  NSLog(@"Unsorted Array === %@", unsortedArray);

  NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]
                                    initWithKey: @"id" ascending: YES];
  NSArray *sortedArray = [unsortedArray sortedArrayUsingDescriptors: [NSArray arrayWithObject:sortDescriptor]];
  NSLog(@"Sorted Array ==== %@", sortedArray);

Answer 3

NSArray is immutable so to sort your array you can replace it with a sorted version like this:

NSArray * myArray = SortArray(myArray);

// SortArray works like this.

// Helper function.
NSInteger MyComparisonFunction(id a, id b, void* context) {
  NSNumber *aNum = (NSNumber*)a[@"id"];
  NSNumber *bNum = (NSNumber*)b[@"id"];
  return [aNum compare:bNum];
}

NSArray* SortArray (NSArray* unsorted) {
  return [unsorted sortedArrayUsingFunction:MyComparisonFunction context:nil];
}

Another method would be to instead use an NSMutableArray and then sort that in a similar way.