Sorting a mutable array using a dictionary key

I am trying to create a simple mutable array with a single key ("dayCounter") that I intend to use for sorting. I've read loads of examples on line, but no joy.

So I create this array. Note the first entry is a NSDictionary object. (The other objects are text)

cumArray = [NSMutableArray arrayWithObjects:[NSMutableArray arrayWithObjects:
                                                         [NSDictionary dictionaryWithObject:[NSString stringWithFormat:@"%i", dayCounter] forKey:@"dayCounter"],[[dailyArray objectAtIndex:x]objec开发者_StackOverflowtAtIndex:0],[[dailyArray objectAtIndex:x]objectAtIndex:1],[[dailyArray objectAtIndex:x]objectAtIndex:2], nil],nil];

I save the array in a plist and everything looks great after the load.

However, when I come to sort the array, the program crashes. I have tried every combination of the following:

        NSSortDescriptor *aSortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"dayCounter" ascending:YES];
        [cumArray sortUsingDescriptors:[NSArray arrayWithObject:aSortDescriptor]];

Do I need a dictionary item to act as a key? Can I sort on the first object any easier? Any help is much appreciated.

Sometimes using too many nested expressions can obscure what's really going on. For example, the 'simple' mutable array you created actually contains a nested mutable array, rather than directly containing the dictionaries you're trying to sort.

So instead of this:

cumArray = [NSMutableArray arrayWithObjects:[NSMutableArray arrayWithObjects:
                                                     [NSDictionary dictionaryWithObject:[NSString stringWithFormat:@"%i", dayCounter] forKey:@"dayCounter"],[[dailyArray objectAtIndex:x]objectAtIndex:0],[[dailyArray objectAtIndex:x]objectAtIndex:1],[[dailyArray objectAtIndex:x]objectAtIndex:2], nil],nil];

try doing this

NSDictionary *dict1 = [NSDictionary dictionaryWithObject:[NSString stringWithFormat:@"%i", dayCounter]
                                                  forKey:@"dayCounter"]
NSArray *objs = [dailyArray objectAtIndex:x];
NSDictionary *dict2 = [objs objectAtIndex:0];
NSDictionary *dict3 = [objs objectAtIndex:1];
NSDictionary *dict4 = [objs objectAtIndex:2];

// Note: You might want to temporarily log the values of dict2 - 4 here to make sure they're
// really dictionaries, and that they all actually contain the key 'dayCounter'.

cumArray = [NSMutableArray arrayWithObjects:dict1, dict2, dict3, dict4, nil];

Assuming that you really have a mutable array of dictionaries, each of which contains the key dayCounter, the sort descriptor you showed in your example should work just fine.

Your setup makes no sense. You are saying yourself that only the first object in the array is a dictionary that contains the key `@"dayCounter" ("The other objects are text"). How is it supposed to be sorted if only one object contains the sort criteria?

You need to sort the array with a method, like - (NSComparisunResult)compareDict If you have to compare 2 dictionaries and determine which one should be ordered above the other ( NSOrderedAscending ) then you need to "extend" NSDictionary:

@interface NSDictionary (SortingAdditions) {}
- (NSComparisonResult)compareTo:(NSDictionary *)other;
@end
@implementation NSDictionary (SortingAddictions)
- (NSComparisonResult)compareTo:(NSDictionary *)other
{
  if( [self count] > [other count] )
  { return NSOrderedAscending; }
}
@end

This method will sort NSDictionaries according to the amount of objects that they contain. Other values you can return here are: NSOrderedDescending and NSOrderedSame.

Then you can sort the mutable array with:

[SomeMutableArray sortUsingSelector:@selector(compareTo:)];

Keep in mind that every object in the array will need to be an NSDictionary, otherwise you will get an exception: unrecognized selector sent to instance blabla

You can do the same thing for any type of object, if the array contains both NSStrings, NSNumbers and NSDictionaries you should take a different approach