Problem with GMT+/- time zones

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)
Should has nothing to do with it. That is the way the Olsen tz database works.  See en.wikipedia.org/wiki/Tz_database.
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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)

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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.
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

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:<jdnewmil at 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 <andrewdigby at 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 at 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.