R help - Dec 2012 - Incorrect DST time changes in DateTimeClasses

Can anyone please shed any light on why R DateTimeClasses give weird times for
when daylight saving time information changes, and which aren't consistent
with the OS?

Example:

	Expected result: in New Zealand DST stopped (NZDT -> NZST) at 03:00 NZDT on
2010-04-04, as confirmed by the OS time zone info (OS X 10.8.2):

	zdump -v /etc/localtime
		/etc/localtime  Sat Apr  3 13:59:59 2010 UTC = Sun Apr  4 02:59:59 2010 NZDT
isdst=1
		/etc/localtime  Sat Apr  3 14:00:00 2010 UTC = Sun Apr  4 02:00:00 2010 NZST
isdst=0

	Result in R: R has DST changing at 02:26:08, instead of 03:00!

	> a<-as.POSIXlt('2010-04-04 02:26:07',tz="NZ")
	> a$isdst
	[1] 1
	> b<-as.POSIXlt('2010-04-04 02:26:08',tz="NZ")
	> b$isdst
	[1] 0


So does R get its DST information from somewhere else? Any suggestions would be
much appreciated!

Thanks

	[[alternative HTML version deleted]]

What OS are you using? It makes a difference.
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Andrew Digby <andrewdigby at mac.com> wrote:
>
>Can anyone please shed any light on why R DateTimeClasses give weird
>times for when daylight saving time information changes, and which
>aren't consistent with the OS?
>
>Example:
>
>	Expected result: in New Zealand DST stopped (NZDT -> NZST) at 03:00
>NZDT on 2010-04-04, as confirmed by the OS time zone info (OS X
>10.8.2):
>
>	zdump -v /etc/localtime
>		/etc/localtime  Sat Apr  3 13:59:59 2010 UTC = Sun Apr  4 02:59:59
>2010 NZDT isdst=1
>		/etc/localtime  Sat Apr  3 14:00:00 2010 UTC = Sun Apr  4 02:00:00
>2010 NZST isdst=0
>
>	Result in R: R has DST changing at 02:26:08, instead of 03:00!
>
>	> a<-as.POSIXlt('2010-04-04 02:26:07',tz="NZ")
>	> a$isdst
>	[1] 1
>	> b<-as.POSIXlt('2010-04-04 02:26:08',tz="NZ")
>	> b$isdst
>	[1] 0
>
>
>So does R get its DST information from somewhere else? Any suggestions
>would be much appreciated!
>
>Thanks
>
>	[[alternative HTML version deleted]]
>
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