[R] bug in as.POSIXct ?

[apjaworski@mmm.com]

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 ?).

Since the only thing the difftime function does is unclass the as.POSIXct
values of its two arguments, the error seems to be in the as.POSIXct code.
I looked at the C code of the as.POSIXct function but I do not know enough
about R code and C handling of the time structures to find an error there.
Perhaps, the error is actually in the C library handling of time structures
on Windows machines.


All this seems to work fine  in version 1.8.1 patched 11-24 on a Linux
machine, i.e. the above difference is 1second.  However, the swicth between
CDT and CSD also accurs at 1:00.


Andy

__________________________________
Andy Jaworski
518-1-01
Process Laboratory
3M Corporate Research Laboratory
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