I have a data set that looks like this for a particular customer:
Date Activity Plan
3/15/2017 Restart 3A
1/1/2016 Signup 2A
I want to calculate and list the months a particular customer was active on a plan. For example, the customer listed in the example above is active during the months of Jan 2016 to Sep 2016 on plan 2A. Then the customer again becomes active between Mar 2017 and Feb 2018 but on a different plan. How do I do that? Please help!