[R] Automatic time zone conversion

[simon]

Hi,

Thanks for the help. Your method does work. However, I am not sure
if my R give CST a correct offset to timezone or at least display it 
normally.
 > cdate
[1] "2000-05-11_01:00:00.0000\005\003"
 > format(as.POSIXct(paste(as.character(strptime(cdate,format=
+"%Y-%m-%d_%H:%M:%S")),"GMT")),tz="CST",format="%Y%m%d %H:%M %Z")
[1] "20000510 17:00 CST"
 > 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"

 > x <- as.POSIXct(chartr("_", " ", cdate), tz = "GMT")
 > attr(x, "tzone") <- NULL
 > x
[1] "2000-05-11 09:00:00 CST"

One thing is strange here. When I tried to find out what the offset is in R.
 > R.version.string
[1] "R version 2.2.0, 2005-10-06"
 > format(Sys.time(),format="%Z %z")
[1] "CST +0000"
While under command line(fedora core 3), my system display a different 
offset.
$date +"%Z %z"
CST +0800

Thanks again for the help and best regard,

Simon

Gabor Grothendieck wrote:

>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
>>
>>______________________________________________
>>R-help at stat.math.ethz.ch mailing list
>>https://stat.ethz.ch/mailman/listinfo/r-help
>>PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>>
>>    
>>
>
>  
>