I'm not surprised that strange things happen if you try to handle times in
the duplicated hour without specifying which time you mean. If your
current time zone setting is something like EST5EDT that includes both
daylight-saving and standard times then 2008-11-02 01:16:00 occured
twice, so some of the calls to difftime() are ambiguous. If your
time-zone setting specifies daylight-saving time or not, then some of the
calls to difftime() involve times that did not exist. If you create
POSIXt objects that unambiguously specify the times then things should be
more predictable.
-thomas
On Fri, 7 Nov 2008, Dennis Fisher wrote:
Colleagues,
I submitted this several days ago and no one responded, so I am trying
again, trying a different subject line:
I just encountered some unexpected behavior of difftime in
relationship to the change from daylight savings to standard time.
My understanding is that DST and ST take effect at 2AM. However, the
results below suggests that R (version 2.8.0 in OS X) implements the
change at 2:16AM:
Expected:
difftime("2008-11-02 02:01:00", "2008-11-02 00:59:00")
Time difference of 2.033333 hours
difftime("2008-11-02 01:16:00", "2008-11-02 01:15:00")
Time difference of 1 mins
difftime("2008-11-02 01:18:00", "2008-11-02 01:17:00")
Time difference of 1 mins
Not expected:
difftime("2008-11-02 01:17:00", "2008-11-02 01:16:00")
Time difference of 1.016667 hours
Can anyone explain this?
Dennis
Dennis Fisher MD
P < (The "P Less Than" Company)
Phone: 1-866-PLessThan (1-866-753-7784)
Fax: 1-415-564-2220
www.PLessThan.com
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[EMAIL PROTECTED] University of Washington, Seattle
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