I'm setting up Enhanced Ecommerce and I was wondering if I need to push a new list of impressions each time a user filters? Is there some kind of logic Google applies that only the last set of impressions is used? The same goes for sorting since I push the position of the product, do I need to sent the sorting method used in order for the position to make sense?
Best practices would like you, for each page, to send to Analytics the impressions that are actually shown to the user, not all of them together on the whole page. If the user scrolls the page and displays a new series of products, then the impressions of those products must be sent. In this way it makes sense to understand the products that the user actually saw.
If you change the order and the display with the filters, in my opinion it should be considered a new page, and send Google Analytics the new display of the products with the correct ordering.
It makes no sense to try to send only the last display of products after the filters, simply because it does not represent reality: that is, the user has seen that product by applying the filter only after it had previously seen other products and was probably not satisfied.