Yes, and sum the attribute counts by the assigned category from the first file.

So if I have 200 items spread equally across 5 categories, I need a sum value for each of the 1 million attributes as they appear in the items grouped by category. So attribute 1 was found 6 times in the 40 items listed as category 1, 12 times in the 40 items listed as category 2...etc, for each category and each attribute.