How to subtract years in R?

Question

I have a date in R, e.g.

dt = as.Date('2010/03/17');

I would like to subtract 2 years from this date, without worrying about leap years and such issues, getting as.Date('2010-03-17'). How would I do that? Thanks!

Answer 1

The easiest thing to do is to convert it into POSIXlt and subtract 2 from the years slot.

> d <- as.POSIXlt(as.Date('2010/03/17'))
> d$year <- d$year-2
> as.Date(d)
[1] "2008-03-17"

See this related question: http://stackoverflow.com/questions/2254986/how-to-subtract-days-in-r.

Answer 2

You could use seq:

R> dt = as.Date('2010/03/17')
R> seq(dt, length=2, by="-2 years")[2]
[1] "2008-03-17"

Answer 3

With lubridate

library(lubridate)
ymd("2010/03/17") - years(2)