Sorting NSMutableArray that contains NSMutableDictionaries [duplicate] - ios

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How do I sort an NSMutableArray with custom objects in it?
(27 answers)
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I'm trying to figure out the best/most efficient way to sort an array that contains n-number of dictionaries. One of the key/value pairs in each dictionary is a date field. After adding all the dictionaries to the array, I would like to sort the array by descending date order.
For example, I have code like this:
NSMutableArray *myArray = [[NSMutableArray alloc] init];
NSMutableDictionary *dictionary1 = [[NSMutableDictionary alloc] init];
NSDate *today = [NSDate date];
[dictionary1 setObject:today forKey:#"date"];
[dictionary1 setObject:#"Another value" forKey:#"anotherKey"];
[myArray addObject:dictionary1];
NSMutableDictionary *dictionary2 = [[NSMutableDictionary alloc] init];
NSDate *tomorrow = [[NSDate date] dateByAddingTimeInterval:60*60*24];
[dictionary2 setObject:tomorrow forKey:#"date"];
[dictionary2 setObject:#"Yet another value" forKey:#"anotherKey"];
[myArray addObject:dictionary2];
Now I need myArray to be sorted by descending date. (array index 0 should be the latest date)
Note: In my actual project, I'm not creating and adding the dictionaries in this way. But for example purposes to see how the date is stored in the dictionary, lets assume I've put these two into the array.

Answer 1

You can use NSSortDescriptors here:
NSMutableArray *myArray = [[NSMutableArray alloc] init];
NSMutableDictionary *dictionary1 = [[NSMutableDictionary alloc] init];
NSDate *today = [NSDate date];
[dictionary1 setObject:today forKey:#"date"];
[dictionary1 setObject:#"Another value" forKey:#"anotherKey"];
[myArray addObject:dictionary1];
NSMutableDictionary *dictionary2 = [[NSMutableDictionary alloc] init];
NSDate *tomorrow = [[NSDate date] dateByAddingTimeInterval:60*60*24];
[dictionary2 setObject:tomorrow forKey:#"date"];
[dictionary2 setObject:#"Yet another value" forKey:#"anotherKey"];
[myArray addObject:dictionary2];
NSSortDescriptor *sortDesciptor = [NSSortDescriptor sortDescriptorWithKey:#"date" ascending:NO];
//Create new sorted array
NSArray *sortedArray = [myArray sortedArrayUsingDescriptors:#[sortDesciptor]];
//Or sort your mutable one
[myArray sortUsingDescriptors:#[sortDesciptor]];

Answer 2

There are lots of ways to do this. You could use an NSSortDescriptor as Krivoblotsky says.
You can also use the NSMutableArray sortUsingComparator method. The code would look something like this:
[myArray sortUsingComparator
^(NSDictionary *obj1, NSDictionary *obj2)
{
return [obj1["date"] compare: obj2["date"]]
}
];
The sortUsingComparator method takes an NSComparator block.
An NSComparator takes two objects of type id, and returns an NSComparisionResult:
typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);
Since NSDate supports the compare method you can just write 1-line comparator block that fetches the date entry for each dictionary and returns the result of comparing them.