How to subtract years?

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('2008-03-17').

How would I do that?

Answer 1

With lubridate

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

Answer 2

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: How to subtract days in R?.

Answer 3

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 4

If leap days are to be taken into account then I'd recommend using this lubridate function to subtract months, as other methods will return either March 1st or NA:

> library(lubridate)
> dt %m-% months(12*2)
[1] "2008-03-17"

# Try with leap day
> leapdt <- as.Date('2016/02/29')
> leapdt %m-% months(12*2)
[1] "2014-02-28"