[R] Automatic time zone conversion

[Gabor Grothendieck]

Note that even that will not reliably work on all platforms.  The
only values for the tz= argument that reliably work across
platforms are tz = "" and tz = "GMT".  (See RNews 4/1 Help Desk.)
In fact, entering the above code into my machine

	> R.version.string  # Windows XP
	[1] "R version 2.2.0, 2005-10-24"

gives a different answer than on your machine:

	> as.POSIXct(as.character(strptime(cdate,format="%Y-%m-%d_%H:%M:%S")),
	+	tz="CST")+(8*3600)
	[1] "2000-05-11 08:00:00 CST"

Also if by CST you mean Central Standard Time as in Chicago, Houston
and Winnipeg then its not 8 hours from GMT.  See:

	http://www.stacken.kth.se/~kvickers/timezone.html


Could it be that you just want to read it in as GMT but
display it in the current time zone?  If so, try this:

	x <- as.POSIXct(chartr("_", " ", cdate), tz = "GMT")
	attr(x, "tzone") <- NULL


On 12/5/05, simon <sentientc at gmail.com> wrote:
> Dear R-help,
>
> I was trying to convert a date and time record extracted from a fortran
> subroutine I worte and I encounter some problem. The data read in time
> and date in a format like "2000-05-11_01:00:00.0000" in fortran output.
> It is in GMT. I need to convert it to CST (GMT+8). I did the following
> steps.
>  > cdate
> [1] "2000-05-11_01:00:00.0000\005\003"
> # I am not sure why the extra characters at the end but it doesn't
> affect the strptime function so I just ingored it.
>  > strptime(cdate,format="%Y-%m-%d_%H:%M:%S")
> [1] "2000-05-11 01:00:00"
> # In order to incoporate GMT into the record, I use paste function to
> stick it in.
>  >as.POSIXct(as.character(strptime(cdate,format="%Y-%m-%d_%H:%M:%S")),tz="GMT")
> [1] "2000-05-11 01:00:00 GMT"
> #It is easier to just do a arthmatic to convert the timezone and ingore
> this attribute like
>  >
> as.POSIXct(as.character(strptime(cdate,format="%Y-%m-%d_%H:%M:%S")),tz="CST")+(8*3600)
> [1] "2000-05-11 09:00:00 CST"
> I was wondering if there is a simpler method to do this.
>
> Thanks in advance,
>
> Simon
>
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