Loading data objects into an NSArray causes a painfully slow startup

I have a Core Data database of about 500 objects. These objects are 'cards' that will be viewed and modified by the user. When a user modifies the card, an attribute called 'groupNumber' will change.

The order of these cards in each group is very important and is determined by the user. I load the database objects into an array. When a user makes a change, I save 开发者_如何学Gothe order of the array into a plist using the 'title' attribute.

My problem comes when the app is relaunched. I need to load the group array in the order it was saved in. But when I use the plist to do a fetch request, it is painfully slow.

The slow code is:

// get array from plist sorted by 'title'
NSMutableArray *group1Temp = [plistData objectForKey:@"group1ArrayData"];

for (int i = 0; i < [group1Temp count]; i++) {
    // set predicate to 'title' attribute
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"title == %@", [group1Temp objectAtIndex:i]];

    // load filtered database object into temp array
    NSArray *temp = [self.vocabDeckArray filteredArrayUsingPredicate:predicate];

    [self.group1Array addObjectsFromArray:temp];
}

When this executes 500 times, it is just too slow. If I could save an NSArray of the database objects themselves into a plist, then I wouldn't need to do a predicate search, but it seems I can't do that.

I'm thinking my entire approach to this has been wrong. How can I save/load the order of an array of database objects in a faster way? Is loading database objects into an array itself bad practice?

Thanks for any help!

Traversing the entire vocabDeckArray and filtering it once for each object in group1Temp is very inefficient. There are any number of ways you could rebuild this sorted data set in less than O(n^2) time.

One easy option might be to store a dictionary with the object's titles as keys and their position in the array as values. That way you can construct an array of known length and put every object in vocabDeckArray into the correct position in a single pass (get first object from vocabDeckArray, lookup where in belongs in group1Array from the dictionary, insert into group1Array, move on to next object). That's still not particularly fast but it seems like a minimal change to your current behavior.

In addition consider the number of method calls within your loop. self.vocabDeckArray and self.group1Array are method calls which you make on every iteration of your loop even though they always return the same objects. Keeping local variables which reference those objects instead would save you the overhead of 2 method calls on every iteration.