On 19/07/2009 11:23 AM, Denis Chabot wrote:
[was " [R] end of daylight saving time"]
Hi,
I got no reply with the previous subject line, probably a bad choice
of subject on my part, so here it is again.
I read from the help on DateTimeClasses and various posts on this list
that, quite logically, one needs to specify if DST is active or not
when time is between 1 and 2 AM on the first Sunday in November (for
North America in recent years).
This I can do for on date at a time:
a <- as.POSIXct("2008-11-02 01:30:00", tz="EST5EDT") # to get
automatic use of DST
b <- as.POSIXct("2008-11-02 01:30:00", tz="EST") # to tell T this is
the second occurrence of 1:30 that day, in ST
difftime(b,a)
Time difference of 1 hours
But why can't I do the following, which appears to be a typical R way
of doing things, to handle several date-times at once?
c <- rep("2008-11-02 01:30:00", 2)
tzone = c("EST5EDT", "EST")
as.POSIXct(c, tz=tzone)
Erreur dans strptime(xx, f <- "%Y-%m-%d %H:%M:%OS", tz = tz) :
valeur 'tz' incorrecte
???
Objects of the POSIXlt and POSIXct classes don't support multiple time
zones, so if you specified several time zones on input, how would the
conversion functions decide which one to use for output? You'll need to
write your own wrapper function to make this decision, and do the
conversions separately for each input timezone.
Why don't those classes support a separate time zone for each entry?
Presumably because their designer never thought anyone would want to do
that.
Duncan Murdoch
Thanks,
Denis Chabot
sessionInfo()
R version 2.9.1 Patched (2009-07-09 r48929)
x86_64-apple-darwin9.7.0
locale:
fr_CA.UTF-8/fr_CA.UTF-8/C/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_2.9.1
______________________________________________
R-help@r-project.org 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.
______________________________________________
R-help@r-project.org 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.
