in reply to
Array of arrays - redux
Why do I have a feeling that the more I read about your problems, the more you should tell us the entire problem you are trying to solve instead of just a small portion of it, and how you have coded that small portion? i.e. why do you have an array of arrays, why do you need to look back over 15 rows, why does the data you are looking for change etc.
If you spot any bugs in my solutions, it's because I've deliberately left them in as an exercise for the reader! :-)