Create end of the month date from a date variable

Question

I have a large data frame with date variables, which reflect first day of the month. Is there an easy way to create a new data frame date variable that represents the last d

Answer 1

library(lubridate)
 as.Date("2019-09-01") - days(1)
[1] "2019-08-31"

or

library(lubridate)
 as.Date("2019-09-01") + months(1) - days(1)
[1] "2019-09-30"