The chron package will do that: > library(chron) > seq(chron("01/31/00"), by = "months", len = 2)[2] [1] 02/29/00
On 10/12/05, Jim Porzak <[EMAIL PROTECTED]> wrote: > OTOH, > > > seq(as.Date("2004-01-31"), by = "month", length = 14) > [1] "2004-01-31" "2004-03-02" "2004-03-31" "2004-05-01" "2004-05-31" > [6] "2004-07-01" "2004-07-31" "2004-08-31" "2004-10-01" "2004-10-31" > [11] "2004-12-01" "2004-12-31" "2005-01-31" "2005-03-03" > > I would prefer to see dates forced to be within each month, not > "leaking" into next month. > > IOW: > [1] "2004-01-31" "2004-02-29" "2004-03-31" "2004-04-30" "2004-05-31", etc > > > -- > Jim Porzak > Loyalty Matrix Inc. > San Francisco, CA > > > > On 10/12/05, Marc Schwartz <[EMAIL PROTECTED]> wrote: > > > Thanks to Prof. Ripley for pointing this out. > > > > > > One of the approaches that I had considered here was to set up a vector > > > of the number of days in each month (adjusting of course for leap > > > years), and use "day arithmetic" to add/subtract the appropriate number > > > of days. > > > > > > However, it was easier to use seq.Date() and to further consider putting > > > a wrapper around it to make it yet even easier to use. > > > > > > Marc > > > > > > On Wed, 2005-10-12 at 13:23 +0100, Prof Brian Ripley wrote: > > > > On Wed, 12 Oct 2005, bogdan romocea wrote: > > > > > > > > > Simple addition and subtraction works as well: > > > > > as.Date("1995/12/01",format="%Y/%m/%d") + 30 > > > > > If you have datetime values you can use > > > > > strptime("1995-12-01 08:00:00",format="%Y-%m-%d %H:%M:%S") + > > > > > 30*24*3600 > > > > > where 30*24*3600 = 30 days expressed in seconds. > > > > > > > > Sorry, not in general, as a month is not generally of 30 days (including > > > > in your example). > > > > > > > > seq.Date is a good way to do this. > > > > > > > > > > > > > > > > > > >> -----Original Message----- > > > > >> From: Marc Schwartz [mailto:[EMAIL PROTECTED] > > > > >> Sent: Tuesday, October 11, 2005 10:16 PM > > > > >> To: t c > > > > >> Cc: r-help@stat.math.ethz.ch > > > > >> Subject: Re: [R] adding 1 month to a date > > > > >> > > > > >> > > > > >> On Tue, 2005-10-11 at 16:26 -0700, 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. > > > > >> > > > > >> There might be an easier way to do this, but using seq.Date(), you > > > > >> can > > > > >> increment or decrement from a Time 0 by months: > > > > >> > > > > >> Add 1 month: > > > > >> > > > > >> This takes your Time 0, generates a 2 element sequence (which begins > > > > >> with Time 0) and then takes the second element: > > > > >> > > > > >>> seq(as.Date("1995-12-01"), by = "month", length = 2)[2] > > > > >> [1] "1996-01-01" > > > > >> > > > > >> > > > > >> > > > > >> Subtract 1 month: > > > > >> > > > > >> Same as above, but we use 'by = "-1 month"' and take the > > > > >> second element: > > > > >> > > > > >>> seq(as.Date("1995-12-01"), by = "-1 month", length = 2)[2] > > > > >> [1] "1995-11-01" > > > > >> > > > > >> > > > > >> See ?as.Date and ?seq.Date for more information. The former > > > > >> function is > > > > >> used to convert from a character vector to a Date class object. Note > > > > >> that in your case, the date format is consistent with the default. > > > > >> Pay > > > > >> attention to the 'format' argument in as.Date() if your dates > > > > >> should be > > > > >> in other formats. > > > > >> > > > > >> HTH, > > > > >> > > > > >> Marc Schwartz > > > > > > ______________________________________________ > > > R-help@stat.math.ethz.ch mailing list > > > https://stat.ethz.ch/mailman/listinfo/r-help > > > PLEASE do read the posting guide! > > > http://www.R-project.org/posting-guide.html > > > > > > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html