Add a Month to a Date

Clueless adding numbers of months to a date will in some cases lead to invalid dates, think of e.g. 2012-01-30 + 1 month.
AddMonths ensures that the result is always a valid date, e.g. as.Date("2013-01-31") + 1 month will be "2013-02-28". If number n is negative, the months will be subtracted.

AddMonths(x, n, ...)

Arguments

x

a Date object (or something which can be coerced by as.Date(x, ...) to such an object) to which a number of months has to be added.

n

the number of months to be added. If n is negative the months will be subtracted.

...

the dots are passed to as.Date, e.g. for supplying origin.

Details

All parameters will be recyled if necessary.

Value

a vector of class Date with the same dimension as x, containing the transformed dates.

References

Thanks to Antonio: https://stackoverflow.com/questions/14169620/add-a-month-to-a-date

Author

Andri Signorell <andri@signorell.net>, based on code by Roland Rapold and Antonio

See also

as.ym; Date functions: Year, Month, etc.

Examples

# characters will be coerced to Date
AddMonths("2013-01-31", 1)
#> [1] "2013-02-28"

# negative n
AddMonths(as.Date("2013-03-31"), -1)
#> [1] "2013-02-28"

# Arguments will be recycled
# (with warning if the longer is not a multiple of length of shorter)
AddMonths(c("2013-01-31", "2013-03-31", "2013-10-31", "2013-12-31"), c(1,-1))
#> [1] "2013-02-28" "2013-02-28" "2013-11-30" "2013-11-30"


x <- as.POSIXct(c("2015-01-31", "2015-08-31"))
n <- c(1, 3)
AddMonths(x, n)
#> [1] "2015-02-28" "2015-11-30"

# mind the origin if x supplied as numeric ...
x <- as.numeric(as.Date(x))
AddMonths(x, n, origin=as.Date("1970-01-01"))
#> [1] "2015-02-28" "2015-11-30"