[R] adding 1 month to a date

[Gabor Grothendieck]

Try this. Note that mapply strips off the class which is why we
set up dd with the correct class and then just replaced the values.

# test data
d <- as.Date("2005-1-1") + seq(0,90,30)

# calculations, dd is the result
next.month <- function(x) seq(x, len = 2, by = "months")[2]
dd <- d
dd[] <- mapply(next.month, dd)


On 10/12/05, t c <quantpm at yahoo.com> wrote:
> Thanks.  How do I use this to calculate a new variable (e.g."data$next_month") from an existing variable (e.g."Data$date_").
>
> I tried : <data$next_month<-seq(as.Date(data$date_), len = 2, by = "month")[2]>,
>
> but get the following error message:   "Error in seq.Date(as.Date(data$date), len = 2, by = "1 month") : 'from' must be of length 1"
>
> Thanks.
>
>
>
> Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
> Try this:
>
> seq(as.Date("2005-01-15"), len = 2, by = "month")[2]
>
> or here is another approach:
>
> http://finzi.psych.upenn.edu/R/Rhelp02a/archive/61570.html
>
> On 10/11/05, t c wrote:
> >
> > Within an R dataset, I have a date field called "date_". (The dates are in the format "YYYY-MM-DD", e.g. "1995-12-01".)
> >
> >
> >
> > How can I add or subtract "1 month" from this date, to get "1996-01-01" or " "1995-11-01".
> >
> >
> >
> >
> >
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