You neglected to update before posting as required by the posting guide.
R 3.0.2 is far from current, and on OS X the timezone internals were
replaced in R 3.1.x (the previous version did not handle 64-bit time_t
correctly, even though that is what OS X uses). And the documentation
is different.
On 21/09/2014 15:39, Denis Chabot wrote:
Sorry, I had not posted in a long time and I remembered this as I pushed the
"send" button.
And I am not surprised that I thought wrong!
I'll start with the missing information:
sessionInfo()
R version 3.0.2 (2013-09-25)
Platform: x86_64-apple-darwin10.8.0 (64-bit)
locale:
[1] fr_CA.UTF-8/fr_CA.UTF-8/fr_CA.UTF-8/C/fr_CA.UTF-8/fr_CA.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] tools_3.0.2
Then I'll admit that some of the very useful details you provided had escaped
me, but in my defense, I took to heart one element found in ?Sys.timezone:
It is not in general possible to retrieve the system's own name(s) for the
current timezone, but Sys.timezone will retrieve the name it uses for the
current time (and the name may differ depending on whether daylight saving time
is in effect).
When I tell my computer that I am in Europe, I get
Sys.time()
[1] "2014-09-21 16:38:45 CEST"
As the output of my "c" also displayed "CEST", I assumed this was the preferred way to
refer to that time zone. Because of this, I had expected c and d to be the same. The output of c is
deceiving. But at least I now know not to use "CEST".
Denis
Le 2014-09-21 à 10:00, Prof Brian Ripley <[email protected]> a écrit :
On 21/09/2014 14:11, Denis Chabot wrote:
Hi,
I have to deal with time-stamped data coming from outside my own time zone, so
the problem is likely poor knowledge of European time zones on my part. But I
am puzzled just the same.
I thought that setting a time zone of "Europe/Copenhagen" would be the same as "CET" in
winter and "CEST" in summer.
You thought wrong: CEST is not a valid timezone on most (maybe all) R platforms.
You failed to tell us the 'at a minimum' information required by the posting
guide. ?Sys.timezone says OlsonNames() tells you the timezone names supported
on your unstated platform, and ?as.POSIXct says
tz: A time zone specification to be used for the conversion, _if
one is required_. System-specific (see time zones), but ‘""’
is the current time zone, and ‘"GMT"’ is UTC (Universal Time,
Coordinated). Invalid values are most commonly treated as
UTC, on some platforms with a warning.
As the posting guide asks, please do your own homework.
This test in winter works as expected:
a = as.POSIXct("2013-02-25 01:00:00", tz="Europe/Copenhagen"); a
[1] "2013-02-25 01:00:00 CET"
b = as.POSIXct("2013-02-25 01:00:00", tz="CET"); b
[1] "2013-02-25 01:00:00 CET"
a-b
Time difference of 0 secs
But this one is summer does not work as I expected:
c = as.POSIXct("2013-07-25 01:00:00", tz="Europe/Copenhagen"); c
[1] "2013-07-25 01:00:00 CEST"
d = as.POSIXct("2013-07-25 01:00:00", tz="CEST"); d
[1] "2013-07-25 01:00:00 UTC"
e = as.POSIXct("2013-07-25 01:00:00", tz="CET"); e
[1] "2013-07-25 01:00:00 CEST"
c-d
Time difference of -2 hours
c-e
Time difference of 0 secs
Setting tz to "Europe/Copenhagen" in summer in c first appears to be the same as setting it to
"CEST" because the output is showing "CEST".
But d should then be the same as c, and it is not.
What is happening?
Thanks in advance,
Denis Chabot
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Brian D. Ripley, [email protected]
Emeritus Professor of Applied Statistics, University of Oxford
1 South Parks Road, Oxford OX1 3TG, UK
______________________________________________
[email protected] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Brian D. Ripley, [email protected]
Emeritus Professor of Applied Statistics, University of Oxford
1 South Parks Road, Oxford OX1 3TG, UK
______________________________________________
[email protected] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
