Exercise

The tricky thing about months

What should ymd("2018-01-31") + months(1) return? Should it be 30, 31 or 28 days in the future? Try it. In general lubridate returns the same day of the month in the next month, but since the 31st of February doesn't exist lubridate returns a missing value, NA.

There are alternative addition and subtraction operators: %m+% and %m-% that have different behavior. Rather than returning an NA for a non-existent date, they roll back to the last existing date.

You'll explore their behavior by trying to generate a sequence for the last day in every month this year.

Instructions

100 XP

We've put jan_31, the date for January 31st this year in your workspace.

  • Start by creating a sequence of 1 to 12 periods of 1 month.
  • Add month_seq to jan_31. Notice what happens to any month where the 31st doesn't exist
  • Now add month_seq to jan_31 using the %m+% operator.
  • Try subtracting month_seq from jan_31 using the %m-% operator.