[R] how to calculate time offset between timezones?

[Armstrong, Whit]

well, strangely,  ISOdatetime(2008,1,1,1,0,0,tz="AST") creates a UTC
timezone date on my system:

> ISOdatetime(2008,1,1,1,0,0,tz="AST")
[1] "2008-01-01 01:00:00 UTC"
> 

and if you compare the numeric values of the UTC datetime and the GMT
datetime, the are definitely the same:

> as.numeric(ISOdatetime(2008,1,1,1,0,0,tz="AST"))
[1] 1199149200
> as.numeric(ISOdatetime(2008,1,1,1,0,0,tz="GMT"))
[1] 1199149200
> 

I think the failure to recognize AST may have something to with the
timzones listed in /usr/share/zoneinfo (on Ubuntu linux) where I found
AST4:

whit at spartan:~$ find /usr/share/zoneinfo -name "AST*"
/usr/share/zoneinfo/SystemV/AST4
/usr/share/zoneinfo/SystemV/AST4ADT
/usr/share/zoneinfo/right/SystemV/AST4
/usr/share/zoneinfo/right/SystemV/AST4ADT
/usr/share/zoneinfo/posix/SystemV/AST4
/usr/share/zoneinfo/posix/SystemV/AST4ADT


and when I use it as the tz argument:

> ISOdatetime(2008,1,1,1,0,0,tz="AST4")
[1] "2008-01-01 01:00:00 AST"
> 

and

> ISOdatetime(2008,1,1,1,0,0,tz="AST4") -
ISOdatetime(2008,1,1,1,0,0,tz="GMT")
Time difference of 4 hours
> 


-Whit


> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of dankelley
> Sent: Thursday, January 10, 2008 10:21 AM
> To: r-help at r-project.org
> Subject: [R] how to calculate time offset between timezones?
> 
> 
> #QUESTION#
> 
> Is there a way to calculate the offset between timezones, 
> e.g. from "AST" to "GMT"?
> 
> #DETAILS# 
> 
> I am working with data files that use local time, and that 
> indicate the timezone by e.g. "AST" (Atlantic Standard Time, 
> my local time) in a header. 
> I was guessing that
> 
> > ISOdatetime(2008,1,1,1,0,0,tz="GMT") -
> > ISOdatetime(2008,1,1,1,0,0,tz="AST")
> 
> would work, but it gives a difference of 0.  However, when I do
> 
> > ISOdatetime(2008,1,1,1,0,0,tz="GMT") - ISOdatetime(2008,1,1,1,0,0)
> 
> I get a -4h offset, which is correct.  The odd thing is, I am 
> in AST time, as shown by the following.
> 
> > ISOdatetime(2008,1,1,1,0,0)
> [1] "2008-01-01 01:00:00 AST"
> 
> #SYSTEM#
> 
> Mac OS X system, with R 2.6.1 
> 
> #PS#
> 
> I am aware that this sort of thing is system dependent, and 
> so there may not be a general solution.  But even if I can 
> only get it working on my own particular system, I'd be happy!
> --
> View this message in context: 
> http://www.nabble.com/how-to-calculate-time-offset-between-tim
> ezones--tp14736453p14736453.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 




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