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 > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ 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