[R] Subtracting number of days from a date
Prof Brian Ripley
ripley at stats.ox.ac.uk
Wed May 26 18:41:22 CEST 2004
On Wed, 26 May 2004, Hoeven, Maarten van der wrote:
> suppose I have a date, say May 15 2004, and I want to now what date it
> is 23 days before that date. The way to calculate the new date should
> (...) take account of leap years :)
>
>
> In pseudocode:
>
> olddate <- "May 15 2004"
> newdate <- olddate-23
>
> I looked around in POSIXct etc..., maybe I overlooked?
olddate <- as.Date("May 15 2004", "%B %d %Y")
newdate <- olddate - 23
newdate
[1] "2004-04-22"
format(newdate, "%B %d %Y")
[1] "April 22 2004"
looks straightforward enough to me (and it knows about leap years).
--
Brian D. Ripley, ripley at stats.ox.ac.uk
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
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