Message-ID: <alpine.LFD.2.00.0911021142240.8823@gannet.stats.ox.ac.uk>
Date: 2009-11-02T11:49:37Z
From: Brian Ripley
Subject: question about difference in date objects
In-Reply-To: <4AEEC2B2.5030108@alumni.albany.edu>
On Mon, 2 Nov 2009, Phil Smith wrote:
> Hi R Community:
>
> I want to take the difference in two dates:
>
> dt2 - dt1.
>
> But, I want the answer in months between those 2 dates.
>
> Can you advise me?
How long is a month?
difftime() can give you an answer in days, which might suffice if you
define a month as a number of days. Another idea is to use (untested)
getMonth <- function(x)
{
xx <- as.POSIXlt(x)
12*xx$year + xx$mon + (xx$mday-1)/31
}
which will convert to a (fractional) number of months since
1900-01-01, and that can be differenced.
> Please respond to: pzs6 at cdc.gov
>
> Thank you!
> Phil Smith
> Centers for Disease Control and Prevention
--
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