Wow. Thanks very much for pointing that out - I never would have guessed it was deliberate that + and - were reversed!
For future reference for anyone else similarly confused by this departure from time zone and mathematic convention, here's the relevant part of en.wikipedia.org/wiki/Tz_database: "The special area of Etc is used for some administrative zones, particularly for "Etc/UTC" which represents Coordinated Universal Time. In order to conform with the POSIX style, those zone names beginning with "Etc/GMT" have their sign reversed from what most people expect. In this style, zones west of GMT have a positive sign and those east have a negative sign in their name (e.g "Etc/GMT-14" is 14 hours ahead/east of GMT.)" Thanks, Andrew On 2/02/2012, at 20:46 , Jeff Newmiller wrote: > Should has nothing to do with it. That is the way the Olsen tz database > works. See en.wikipedia.org/wiki/Tz_database. > --------------------------------------------------------------------------- > Jeff Newmiller The ..... ..... Go Live... > DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go... > Live: OO#.. Dead: OO#.. Playing > Research Engineer (Solar/Batteries O.O#. #.O#. with > /Software/Embedded Controllers) .OO#. .OO#. rocks...1k > --------------------------------------------------------------------------- > Sent from my phone. Please excuse my brevity. > > Andrew Digby <andrewdi...@mac.com> wrote: > >> >> I'm struggling with time zone version when expressed as hours offset >> from GMT. Can anyone confirm that the behaviour below is incorrect? It >> seems that the GMT offsets are backwards: >> >>> format(as.POSIXct("2011-05-23 17:23:00", >> tz="Europe/London"),tz="America/New_York",usetz=T) >> [1] "2011-05-23 12:23:00 EDT" >> >> - this works. >> >>> format(as.POSIXct("2011-05-23 17:23:00",tz="GMT"),tz="GMT-5",usetz=T) >> [1] "2011-05-23 22:23:00 GMT" >> >> - this doesn't work: 17:23:00 GMT should be 12:23:00 GMT-5! >> >> >> Thanks. >> >> >> R version 2.13.0 (2011-04-13) >> Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit) >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.