From ripley@stats.ox.ac.uk  Wed Feb 26 13:13:02 2003
From: ripley@stats.ox.ac.uk (ripley@stats.ox.ac.uk)
Date: Wed Feb 26 13:13:02 2003
Subject: [Rd] POSIX problem in New Zealand (PR#2570)
In-Reply-To: <Pine.A41.4.44.0302211929050.95120-100000@dante24.u.washington.edu>
Message-ID: <Pine.LNX.4.44.0302261209440.21601-100000@gannet.stats>

We can't reproduce the `bug' on an XP machine in the NZ timezone!
Indeed, there is no bug in the output you present, just different time 
zones.

I did find a bug in the code which gave me different answers from you, and 
fixed it in R-devel.  Please take a look at the current R-devel snapshot 
and see if it gives you what you want.

On Fri, 21 Feb 2003, Arni Magnusson wrote:

> 
> 
> On Fri, 21 Feb 2003 ripley@stats.ox.ac.uk wrote:
> 
> > What exactly is the problem?  Those appear to be the same time, in
> > different time zones.  Is the problem that you are in the N Hemisphere
> > (your email address is) trying to use S Hemisphere times on an OS that
> > does not support pre-1970 times?
> 
> Currently I'm in New Zealand working on a Windows XP machine that has
> never left the country. I have not encountered problems with as.POSIXct
> when working in other time zones.
> 
> 
> > You seem to be confusing the time and how it is printed.  What do you
> > want to do with these times?
> 
> I'm dealing with two kinds of problems: (1) what I see as a bug in
> as.POSIXct, and (2) my own confusion with time zones. One problem at a
> time:
> 
> 
> (1) as.POSIXct
> 
> I would like the following to return similar times, except for the year,
> but they don't:
>  > x <- as.POSIXct("1969-12-24")
>  > y <- as.POSIXct("1970-12-24")
>  > x
>  [1] "1969-12-23 23:00:00 New Zealand Standard Time"
>  > y
>  [1] "1970-12-24 New Zealand Standard Time"
>  > z <- seq(x, by="year", length=2)[2]
>  > difftime(y, z)
>  Time difference of 1 hours
> 
> >From reading 'library/base/html/DateTimeClasses.html' I understand that R
> queries Windows XP for the period 1970-2037 and uses its own C code
> outside this range. To me it looks like the bug might be in the C code. I
> think the problem goes deeper than print.POSIXct, because coercions are
> independent of the print method as far as I understand:
> 
>  > x <- as.POSIXlt("1969-12-24")
>  > y <- as.POSIXlt(as.POSIXct(x))
>  > x
>  [1] "1969-12-24"
>  > y
>  [1] "1969-12-23 23:00:00 New Zealand Standard Time"
>  > x==y
>  [1] FALSE
> 
> 
> (2) Time zone confusion
> 
> This is a question of taste and implementation, but I would like POSIXct
> objects in data frames and plots to display the times I entered
> originally, regardless of where in the world I'm working at the moment.
> 
> 
> (3) My solution
> 
> I've defined the environment variable tz=GMT in my R shortcut and I'll try
> to remember doing so on other machines I work on. This way I avoid both
> the as.POSIXct/New Zealand bug and the time zone confusion. I still think
> the Kiwis would appreciate the bug being fixed :)
> 
> 
> 
> 
> > On Fri, 21 Feb 2003 arnima@u.washington.edu wrote:
> >
> > > Full_Name: Arni Magnusson
> > > Version: 1.6.2
> > > OS: Windows XP
> > > Submission from: (NULL) (210.48.49.68)
> 
> 

-- 
Brian D. Ripley,                  ripley@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



[Rd] POSIX problem in New Zealand (PR#2570)
ripley@stats.ox.ac.uk