Rank within double grouping - possible?

Hey,

I'm trying to add a rank column to a fact table that ranks based on two groupings.

My table basically contains records for user activities with user id, created date and a column with the product id for which the activity happend.

It looks like this:

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What I now want to do is to create a column that ranks the activities by created date, based on user AND product.

How can I do this?

Thanks!