POSIX and summer savings time redux

Thu, Dec 7, 2006 3:09 AM

CET is not a valid timezone *on Windows*: please do RTFM.
E.g. ?Sys.timezone says

      'Sys.timezone' returns an OS-specific character string, possibly
      an empty string.  It may be possible to set the timezone via the
      environment variable '"TZ"': see 'as.POSIXlt'. Windows is
      notorious for naming its timezones differently from the official
      names.

and ?as.POSIXlt points you at

      a specification of the form 'GST-1GDT',

which seems to be the same as CET, and that works on my Windows laptop.
It is also possible that tz="" works for you: it seems to for me when I 
set my machine to CET.

On Thu, 7 Dec 2006, Derek Eder wrote:

When I tried Professor Ripley's example (below), the "tz" argument
failed to adjust clock time from UTC.

(z <- ISOdatetime(1970,1,1,0,0,0, tz="UTC")+1165398135729/1000)

[1] "2006-12-06 09:42:15 UTC"

format(z, "%Y-%m-%d %H:%M:%OS3",tz = "CET")

[1] "2006-12-06 09:42:15.729"
# expected CET (Central European Time) clock time is UTC + 1 hour time
zone adjustment


Am I running into platform dependencies?

(my platform)
platform       i386-pc-mingw32
arch           i386
os             mingw32
system         i386, mingw32
status
major          2
minor          4.0
year           2006
month          10
day            03
svn rev        39566
language       R
version.string R version 2.4.0 (2006-10-03)


Thank you most sincerely,

Derek Eder



Prof Brian Ripley wrote:

On Wed, 6 Dec 2006, Derek Eder wrote:

I have a time stamp in UTC (GMT) time:

 format(ISOdatetime(1970,1,1,0,0,0)+1165398135729/1000,"%Y-%m-%d

%H:%M:%OS3")

"2006-12-06 09:42:18.823"  (note millisecond accuracy, but not relevant
to question here)

But it is the wrong answer, and not what my system gives.

Now, this time stamp actually "happened" at local (Swedish) time one
hour later (10:42).

So you need to tell R that it was in UTC, which is what the 'tz'
argument is for:

(z <- ISOdatetime(1970,1,1,0,0,0, tz="UTC")+1165398135729/1000)

[1] "2006-12-06 09:42:15 UTC"

format(z, "%Y-%m-%d %H:%M:%OS3", tz="CET")

[1] "2006-12-06 10:42:15.729"

Regarding summer/winter adjustments in time ("spring forward, fall
back"):   Is there a way of automatically recovering the local time
adjustments for a given date?  E.g., a date/time in springtime = GMT +2
, else GMT +1

Is the above not enough?  You can unpick it if you want to get the shift.

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

POSIX and summer savings time redux

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