Calculating days per month between interval of two dates

Question

I have a set of events that each have a start and end date, but they take place over the scope of a number of months. I would like to create a table that shows the number of

Answer 1

This is not necessarily efficient because it creates a sequence of days, but it does the job:

> library(zoo)
> table(as.yearmon(seq(event_start_date, event_end_date, "day")))

Oct 2012 Nov 2012 Dec 2012 Jan 2013 Feb 2013 
       9       30       31       31        7

If your time span is so large than this method is slow, you'll have to create a sequence of firsts of the months between your two (truncated) dates, take the diff, and do a little extra work for the end points.