On Fri, 23 Apr 2004, Vadim Ogranovich wrote: > Thank you for the lead, Dirk! Indeed this works on my machine too: > > > as.POSIXct("2000-05-10 10:15:00", tz="PST8PDT") - > as.POSIXct("2000-05-10 10:15:00", tz="GMT") > Time difference of 7 hours > > > However when I replace POSIXct by POSIXlt it breaks (this looks like a > bug to me): > > > as.POSIXlt("2000-05-10 10:15:00", tz="PST8PDT") - > as.POSIXlt("2000-05-10 10:15:00", tz="GMT") > Time difference of 0 secs
No, it's not a bug. POSIXlt times are just numeric representations of broken-down times, and the tzone attribute (which is normally not present) is just a reminder to you. (It has not been checked, so this is avoid nasty surprises if it is wrong.) Maybe it was a bad idea to allow - for POSIXlt times, but then we do expect users to read the documentation (including the code if they are puzzled). > Now a couple of new questions: > * how could I learn about appropriate names for time zones? For example > I was using "PST" whereas it seems I had to use either "PST8" or > "PST8PDT". Why "PST" was not good? Is it documented anywhere? Specific to your OS, so I expect it documents it somewhere. > * there seems to be no difference betweeen GMT and BST on my machine > though PST8 and PST8PDT are treated properly: > > # PST8 is not identical to PST8PDT > > ISOdatetime(2003, seq(12), 1, 10, 0, 0, tz="PST8") - ISOdatetime(2003, > seq(12), 1, 10, 0, 0, tz="PST8PDT") > Time differences of 0, 0, 0, 0, 3600, 3600, 3600, 3600, > 3600, 3600, 0, 0 secs > > # GMT0 is identical to BST > > ISOdatetime(2003, seq(12), 1, 10, 0, 0, tz="GMT0") - ISOdatetime(2003, > seq(12), 1, 10, 0, 0, tz="BST") > Time differences of 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 secs > > Why is such dichotomy? Ask your OS designer - timezones are handled by your OS. I would not consider "BST" to be a timezone as it is only defined for half the year. Windiows thinks I am on `GMT Daylight Time' although that usage is otherwise unknown in this country. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html