POSIX problem in New Zealand (PR#2570)

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)