Firebase Analytics Filter By User ID
I have spent a few hours on this and found the answer i was looking for more or less, hopefully this might save someone else some time.
The only way to filter by Firebase's User Id property is by creating an audience, there you will be able to pick the user id property that is supplied from the setUserId(String id) method.
It is a downer though because you won't see any events for the user/user's you want from before the audience was created.
I was scratching my head with this issue. Initially, I felt so dumb when I could not find how to use user id for filtering in Firebase analytics dashboard that I am setting with official API setUserId(). When I try to look for answer, I realized that I am not the only one. Finally, this is how I was able to filter events based on user id.
In Android Code, I set user id using setUserId() method. When I read bigQuery has this property as user_id, I thought to give it a try by adding a new user property in Firebase Dashboard with the hope that it will fetch the reported id. 
And... that worked...Now I can filter new events based on user id.
