R help - Dec 2006 - POSIX and summer savings time

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)

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

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

Thanks,

Derek Eder


-- 
Derek N. Eder

Gothenburg University 
VINKLA - Vigilance and Neurocognition laboratory 

SU/Sahlgrenska
Utvecklingslab 1, Med
Gr?na str?ket 8
SE 413 45 G?teborg (Gothenburg)
Sverige (Sweden)

+46 (031)* 342 8261 (28261 inom Sahlgrenska)
+46 0704 915 714 (mobile)
+46 (031) 25 97 07 (home)

* omit the 0 when calling from outside Sweden

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