R：基于来源日期范围的每月分档

Binning examples for R I've found seem to assume the source data has a single date (or date/time). I've discrete start and stop dates for user accounts ranging over years 2002-2017. I want to output counts of the number of accounts active, using monthly bins, during the overall range 2002-17. Binning examples for R I've found seem to assum