Question

Say I have a collection of “node” instances. An integer property call zIndex will be used to group them.

What are the pros/cons for storing them in :
1) An array of arrays
2) A dictionary of arrays

In pseudo code, I would describe the expected result like this:

zBuffer[100] = [node1, node 2];
zBuffer[105] = [playerNode, collectable1];
zBuffer[110] = [foreground1, foreground2];

And I’m wondering about what zBuffers should be; Must NSArrays only be used for sequential read/write? Like not using non-continuous indexes?

I tried with an NSMutableArray:

[zBuffer objectAtIndex:zOrder]

But it fails if the array contains no data for that index (like out-of-bound exception).

Thanks for your advices!
J

Answer 1

As far as I can see, one of your requirements is that the indexes you use to access zBuffer be not contiguous (100, 105, 100). In this case, I would not use an array for that, since the indexes you can use with an array must be less than the count of elements of the array (if you have 3 elements, then indexes range from 0 to 2).

Instead I would use NSMutableDictionary, where you can use the zIndex key as a “name” for groups of objects you are looking for.

This suggestion does not take into account any other requirements that you might have, especially concerning complexity and the kind of operations you are going to carry through on your collection of nodes (beyond accessing them through zIndex).