POSIX and summer savings time redux

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

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.

Derek N. Eder

Gothenburg University 
VINKLA - Vigilance and Neurocognition laboratory 

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