I want to know how to use aggregate() to take all of the objects of a specific field (i.e. "user") and count them.

This what I am doing:

I want to return a list of users with the sum of how many tweets that have made?

So I want output that looks like

Etc..

Also I don't want repeating users like

Etc..

which is what the above aggregate does.

So basically, how can I modify this aggregate to ensure the objects are unique?