How to sort feed aggregator's items in Views according to its category?
I'm hoping you've answered the question by now but just in case, I'll answer it for anyone who comes looking for it.

(Drupal 7)
If you only have two feed categories then after creating your aggregator view, add the "Aggregator Category: Category" field to your view. Make sure to check 'exclude from display' or it will show the category title in duplicates. Then, go up to your format settings of the view and add "Aggregator Category: Category" to "Grouping field Nr.1." This will sort and split your feed items into the different categories.

If you have several feed categories and only want to use two of them, you would add the filter "Aggregator Category: Category ID" with the values 1 and 2, or whatever the category ID is of the category you want. Then repeat the steps above.