In this xlsx (link: https://drive.google.com/open?id=1agN53t1bX8qxCpFGqTOAdHIV_tcBW8ih), I want to find out the following.
For each item listed, I want to know a unique count based on month-year. I.e., for item 4656541653, the count for January 2017 would = 1, December 2017 = 1, November 2017 =...