Getting Top 10 Highest Numbers From Array?

Question

I am having a bit of a issue. I have an NSMutableDictionary with 10 NSMutableArrays in it. Each array has somewhere between 0-10 numbers which could each be any integer, e.g. 12

Answer 1

Sounds like some sort of homework :)

So you have this:

NSMutableDictionary* source = [@{
    @"1" : @[ @10, @20, @100 … ],
    @"2" : @[ @8, @42, @17 … ]
} mutableCopy];

So lets start by creating another arrangement:

NSMutableArray* numbers = [NSMutableArray new];
for (NSArray* array in source.allValues)
{
    for (NSNumber* number in array)
    {
        [numbers addObject: @{ @"number" : number, @"parent" : array }];
    }
}

This is what we get:

@[
    @{ @"number" : @10, @"parent" :  },
    @{ @"number" : @20, @"parent" :  },
    …
]

Now we can sort and find the numbers you wanted.

[numbers sortUsingComparator: ^( id lhs, id rhs ){
    return [((NSDictionary*) rhs)[@"number"] compare: ((NSDictionary*) lhs)[@"number"]];
}];
NSArray* topNumbers = [numbers subarrayWithRange: NSMakeRange( 0, 10 )];

Here we are. topNumbers contains the numbers you needed along the source array.

This is quite a naive way to do it. It can be optimized both in CPU time and memory usage by a fair amount. But hey, keep it simple is not a bad thing.

Not addressed: what if the tenth and eleventh numbers are equal? (adressed here: Pick Out Specific Number from Array?) range checks. not tested, not even compiled. ;)