Sort array of dictionaries with NSNumbers - ios

Question

I have array which has dictionaries. each dictionary is :
NSDictionary *imageAndIndex=[[NSDictionary alloc] initWithObjectsAndKeys:image,[NSNumber numberWithLong:index], nil];
Where the object is image, and the key is NSNumber key made from index.
I want to sort the array according to the NSNumbers indexes so it will become:
0,1,2,3,4 ..
How can i use NSSortDescriptor ?

Answer 1

The problem (and the debate herein) is complicated by two factors: 1) The OP design choice to sort based on a dictionary key, rather than on a value. #sooper in comments pointed out correctly that the better design would be to add a #"sortBy" key, whose value is the NSNumber to be sorted. 2) The second complication is the question's reference to NSSortDescriptor, which is going to depend upon values for a given key, not the key itself.
I think the right answer is to take the #sooper suggestion to add #"sortBy" key-value pairs, but if you must sort the data as is...
- (void)sortDictionaries {
NSDictionary *d0 = #{ #0: someUIImage0};
NSDictionary *d1 = #{ #1: someUIImage1};
NSDictionary *d2 = #{ #": someUIImage2};
NSArray *unsorted = #[d1, d2, d0];
NSArray *sorted = [unsorted sortedArrayUsingComparator:^(NSDictionary *obj1, NSDictionary *obj2) {
NSNumber *key1 = [self numericKeyIn:obj1];
NSNumber *key2 = [self numericKeyIn:obj2];
return [key1 compare:key2];
}];
NSLog(#"%#", sorted);
}
- (NSNumber *)numericKeyIn:(NSDictionary *)d {
// ps. yuck. what do we want to assume here?
// that it's a dictionary?
// that it has only one key value pair?
// that an NSNumber is always one of the keys?
return [d allKeys][0];
}
Not sure why we had to handle this with so much ill-temperment. It's programming, it's supposed to be fun!
Anyway, here's how you'd do it with a sort key and sort descriptor:
- (void)betterSortDictionaries {
NSDictionary *d0 = #{ #"image":image1, #"sortBy":#0 };
NSDictionary *d1 = #{ #"image":image2, #"sortBy":#1 };
NSDictionary *d2 = #{ #"image":image3, #"sortBy":#2 };
NSArray *unsorted = #[d1, d2, d0];
NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:#"sortBy" ascending:YES];
NSArray *sorted = [unsorted sortedArrayUsingDescriptors:#[descriptor]];
NSLog(#"%#", sorted);
}