[R] problem with as.POSIXct and daylight savings time

[Denis Chabot]

[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

???

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