Question

I have the following problem: i have an array of integers and I would like to put them in a data structure that will have each integer with the numbers of its occurrences, and then sort by the number of occurrences.

So if I have:

[1, 3, 4, 6, 6, 3, 1, 3]

I will have:

[(4,1), (6,2), (1,2), (3,3)]

Where (x,y) == (integer, count of its occurrences).

I tried to use NSCountedSet but it doesn’t work well and I was wondering what’s the best way to do that.

So far I have done the following:

NSCountedSet *totalSet = [[NSCountedSet alloc] initWithArray:finalArray];

Where finalArray is the final array with the full raw data not sorted. totalSet is grouped into (x,y) but not sorted (ideally, should be sorted by ‘y’).

I also tried to do this, but it did not work:

NSArray *sortedArray = [finalArray sortedArrayUsingSelector:@selector(compare:)];

And then do:

NSCountedSet *totalSet = [[NSCountedSet alloc] initWithArray:finalArray];

But that did not change ‘totalSet’.

Answer 1

You could put the numbers and their counts in to an array of dictionaries Like this:

    NSArray *arr = @[@1, @3, @4, @6, @6, @3, @1, @3];
    NSCountedSet *totalSet = [NSCountedSet setWithArray:arr];
    NSMutableArray *dictArray = [NSMutableArray array];
    for (NSNumber *num in totalSet) {
        NSDictionary *dict = @{@"number":num, @"count":@([totalSet countForObject:num])};
        [dictArray addObject:dict];
    }
    NSArray *final = [dictArray sortedArrayUsingDescriptors:@[[NSSortDescriptor sortDescriptorWithKey:@"number" ascending:YES ]]];
    NSLog(@"%@",final);