NSMutableArray Sorting and grouping with memory Optimisation - objective-c

Question

NSArray has ItemObject's in it. This ItemObject's are not grouped based on ItemID
The Sample of the json is displayed below:
You will note the itemIDs "a123","a124". There can be n number of itemIDs.
[
{
"ItemName": "John",
"ItemID": "a123"
},
{
"ItemName": "Mary",
"ItemID": "a124"
},
{
"ItemName": "Larry",
"ItemID": "a123"
},
{
"ItemName": "Michel",
"ItemID": "a123"
},
{
"ItemName": "Jay",
"ItemID": "a124"
}
]
The above response is stored in NSArray as follows:
NSMutableArray *itemArray=[[NSMutableArray alloc] init];
ItemObject *obj=[[ItemObject alloc] init];
obj.itemName=#"John";
obj.itemID=#"a123";
[itemArray addObject:obj]
.....
ItemObject *objN=[[ItemObject alloc] init];
objN.itemName=#"Jay";
objN.itemID=#"a124";
[itemArray addObject:objN].
This shows, if there are N items in JSON, then it will create a array of N items.
The above item is displayed correctly in UItableView.
Now, if want to sort them and put them in NSMutableArray group wise what will be optimal way to code it, with less memory footprint to be consumed. [i.e sorting + grouping]
I am trying to achieve the below:
NSMutableArray *itemArray=[[NSMutableArray alloc] init];
at index 0: NSArray with itemID "a123"
at index 1: NSArray with itemID "a124"
Since, available ItemIds, are dynamic, as I explained there can be "N" number of itemId's.
Step 1:
So, I first need to find the available itemId's.
Step 2:
NSMutableArray *myArray=[[NSMutableArray alloc] init];
for(NSString *itemID in itemIDS){
NSArray *itemsForID=[itemArray filterUsingPredicate:[NSPredicate predicateWithFormat:"itemID MATCHES %#",itemID]];
[myArray addObject:itemsForID];
}
myArray is the expected result.
But using filterUsingPredicate "N" number of times will be time and memory consuming.
Any, help Appreciated.

Answer 1

Can you please try the below code?
NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:#"itemID" ascending:YES];
[itemArray sortedArrayUsingDescriptors:[NSArray arrayWithObjects:descriptor,nil]];

Answer 2

You could persist your data as NSManagedObjects. Then you can use an NSFetchedResultsController as data source for your table (you set a sort descriptor and a section name key path to it):
NSFetchedResultsController *controller = [[NSFetchedResultsController alloc]
initWithFetchRequest:fetchRequest
managedObjectContext:context
sectionNameKeyPath:nil
cacheName:nil];
You can also set the batch size (the max number of objects taken from the DB at a time).
Hope this helps!