rails getting count of rows per user per date in activerecord sqlite

I'm starting out with an Activities table that looks like the one below and I'd like to get a count for activities per user per month. The issue is right now, there are multiple rows per day for each user. I need to count only one row per day for each user.

Activities

Activity_id  |   user_id |  activity_type |  created_at

1                  1          time_trial        2016-04-30
2                  1          time_trial        2016-04-30
3                  1          time_trial        2016-04-31
4                  3          time_trial        2016-04-31
5                  3          time_trial        2016-04-31
6                  1          time_trial        2016-04-32

I figure the resulting table should something like

user_id  |   activities per month

1                  3
3                  1