Question

I have an NSArray containing several NSDictionary instances. Each NSDictionary has, among other fields, an object named rating and one numberOfVotes(both are int). How can I sort the array so it gets sorted by rating/numberOfVotes? More generically, can I sort it by doing an operation like mentioned above? Or would it be better to just add another object to each NSDictionary with the value of each operation and then sort by that?

Thanks

EDIT – I have added the following. Still not sorting properly. One question: Should this work for more than 2 objects in my array. (The number of objects will vary)

    [sortedArray sortedArrayUsingComparator:^NSComparisonResult(id dict1, id dict2)
{
    MyObj *obj1 = (MyObj *)dict1;
    MyObj *obj2 = (MyObj *)dict2;

    int rating1 = obj1.rating.intValue;
    int rating2 = obj2.rating.intValue;

    int number1 = obj1.number_of_votes.intValue;
    int number2 = obj2.number_of_votes.intValue;

    double key1 = ((double)rating1)/number1;
    double key2 = ((double)rating2)/number2;

    if (key1 < key2)
    {
        return NSOrderedDescending;
    }

    if (key2 < key1)
    {
        return NSOrderedAscending;
    }
    return NSOrderedSame;

}];

Answer 1

You can define a custom comparator to use a composite sorting key of the kind that you are looking for. If there is no good reason to have that sorting key in the dictionary, other than performing the sort, do not add an item to the dictionary.

array = [array sortedArrayUsingComparator: ^(id obj1, id obj2) {
    int rating1 = [[obj1 objectForKey:@"rating"] intValue];
    int numberOfVotes1 = [[obj1 objectForKey:@"numberOfVotes"] intValue];
    int rating2 = [[obj2 objectForKey:@"rating"] intValue];
    int numberOfVotes2 = [[obj2 objectForKey:@"numberOfVotes"] intValue];
    double key1 = ((double)rating1)/numberOfVotes1;
    double key2 = ((double)rating2)/numberOfVotes2;
    if (key1 > key2) {
        return (NSComparisonResult)NSOrderedDescending;
    }

    if (key1 < key2) {
        return (NSComparisonResult)NSOrderedAscending;
    }
    return (NSComparisonResult)NSOrderedSame;
}];

Note: The sortedArrayUsingComparator: method does not sort the array in place; instead, it returns a sorted copy. If you would like an in-place sorting, use NSMutableArray.