Sort NSMutableArray with custom objects by another NSMutableArray [duplicate]

Question

I have 2 NSMutableArrays. First array contains custom object intances with property NSString *itemID, second array contains only from NSString objects with same values of itemID, but in another order. I need to sort first array by itemID property of each object, and it should be sorted like second array.

How I can do this?

Answer 1

guideArray = < YOUR SECOND ARRAY WITH STRING OBJECT >;    
unsortedArray = < YOUR FIRST ARRAY WITH CUSTOM OBJECT >;

[unsortedArray sortUsingComparator:^(id o1, id o2) {
    Items *item1 = o1;
    Items *item2 = o2;
    NSInteger idx1 = [guideArray indexOfObject:item1.ItemID];
    NSInteger idx2 = [guideArray indexOfObject:item2.ItemID];
    return idx1 - idx2;
}];
NSLog(@"%@",unsortedArray);

Answer 2

Store the custom objects in an dictionary with itemID as key, use this dictionary as lookup to sort the objects:

    NSArray *objects; // your objects
    NSMutableArray *hintArray; // your sorted IDs
    NSMutableDictionary *lookupDict = [[NSMutableDictionary alloc] initWithCapacity:[objects count]];
    NSMutableArray *sortedObjects = [[NSMutableArray alloc] initWithCapacity:[hintArray count]];

    for (id object in objects) {
        [lookupDict setValue:object forKey:[object itemID]];
    }

    for (id hint in hintArray) {
        [sortedObjects addObject:[lookupDict valueForKey:hint]];
    }

EDIT: Solution with inplace sort of objects:

    NSMutableArray *objects;
    NSMutableArray *hintArray;
    NSMutableDictionary *lookupDict = [[NSMutableDictionary alloc] initWithCapacity:[hintArray count]];

    int i = 0;
    for (NSString *itemID in hintArray) {
        [lookupDict setValue:[NSNumber numberWithInt:i] forKey:itemID];
        i++;
    }

    [objects sortUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        return [[lookupDict valueForKey:[obj1 itemID]] compare:[lookupDict valueForKey:[obj2 itemID]]];
    }];