I think that there is a bug in the as.POSIXct function on Windows.
Here is what I get on Win2000, Pentium III machine in R 1.8.1.
dd1 <- ISOdatetime(2003, 10, 26, 0, 59, 59) dd2 <- ISOdatetime(2003, 10, 26, 1, 0, 0) dd2 - dd1
Time difference of 1.000278 hours
Now, the 26th of October was the day that change to the standard time occurred, so I suspect that this has something to do with that. In fact
dd1
[1] "2003-10-26 00:59:59 Central Daylight Time"
dd2
[1] "2003-10-26 01:00:00 Central Standard Time"
so it looks like the switch from CDT to CST happens at 1:00 (instead of 2:00 ?).
Or, it did happen at 2:00 CDT, when the time fell back one hour to 1:00 CST. 1:00 am occured twice on that day, once as CDT and once as CST. R picked the last one. A bit pathological at first glance, but date-handling often is.
As for the dd2 - dd1 value, the "correct" value depends which 1:00 am was chosen. On Windows, this should be 1 hour, 1 second, no? I'm thinking 1:00 am CST == 2:00 am CDT, so in CDT entirely, your expression is basicly 02:00:00 CDT - 00:59:59 CDT.
This makes me suspect that Linux picked the former 1:00 am, from your report. Since R gets its date intricacies from the OS, there really isn't much that can be done about this, until someone builds a full POSIX time implementation that takes all the world's locales and time zones into account, and welds it into R. Volunteers?
It's things like this that make me convert everything to UCT (GMT, or Zulu, if you prefer). Not R's fault; stupid calendar tricks are to blame here.
Cheers
Jason -- Indigo Industrial Controls Ltd. http://www.indigoindustrial.co.nz 64-21-343-545 [EMAIL PROTECTED]
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