[R] Timezone issue with strftime/strptime and %z and %Z

[David Winsemius]

On Mar 10, 2011, at 8:46 PM, David Winsemius wrote:

>
> On Mar 10, 2011, at 11:17 AM, Daniel Nüst wrote:
>
>> Hello!
>>
>> I've been trying to get this right for quite a while now and fear
>> there is an easy solution I just don't see. I did not have this
>> problem in Linux, and I searched r-help and Google but did not find a
>> solution, but of course I am grateful for and resources I might not
>> have found our not understood yet.
>>
>> I try to parse a time stamp with time zone. I essentially just want  
>> to
>> parse the time stamp "1995-05-25T15:30:00+10:00" and output it  
>> exactly
>> like it is, using the POSIX classes (or is that impossible?).
>
> Does this work?
>
> as.POSIXlt(gsub("T.*(\\+|\\-)..(:)", "", # get rid of the colon in  
> the tz
>           # but preserve the sign for the %z format string
>           gsub("T", " ", "1995-05-25T15:30:00-1000")), # replace the  
> "T" with a space
>            format="%Y-%m-%d %H:%M:%S%z")

Daniel;

That example didn't have the full complexity of the question so I  
didn't notoce that I had incorrectly constructed a regex OR within the  
colon handling clause. I neverdid figure out how to do that properly,  
but htis should handle it:

as.POSIXlt(gsub("T", " ", #change T to space
+           # but preserve the sign for the %z format string
+           gsub("(T..:..:.....):", "\\1",  
"1995-05-25T15:30:00-10:00")),  format="%Y-%m-%d %H:%M:%S%z")
[1] "1995-05-25 21:30:00"

To get output in GMT add tz argument to as.POSIXlt:

 > as.POSIXlt(gsub("T", " ", #change T to space
+           # but preserve the sign for the %z format string
+           gsub("(T..:..:.....):", "\\1",  
"1995-05-25T15:30:00-10:00")),  format="%Y-%m-%d %H:%M:%S%z", tz="GMT")
[1] "1995-05-26 01:30:00 GMT"

-- 
David.

>>
>> Please find the script and output/comments below.
>>
>> Regards,
>> Daniel
>>
>>
>>> sessionInfo()
>> R version 2.12.1 (2010-12-16)
>> Platform: x86_64-pc-mingw32/x64 (64-bit)
>>
>> locale:
>> [1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252
>> [3] LC_MONETARY=German_Germany.1252 LC_NUMERIC=C
>> [5] LC_TIME=German_Germany.1252
>>
>> attached base packages:
>> [1] stats     graphics  grDevices utils     datasets  methods   base
>>
>> other attached packages:
>> [1] rj_0.5.2-1
>>
>> loaded via a namespace (and not attached):
>> [1] rJava_0.8-8  tools_2.12.1
>>>
>>> t1 <- strptime("1995-05-25T15:30:00+10:00", format = "%Y-%m-%dT%H: 
>>> %M:%OS")
>>> t2 <- strptime("1995-05-25T15:30:00+10:00", format = "%Y-%m-%dT%H: 
>>> %M:%OS%z")
>>>
>>> strftime(t1, format = "%Y-%m-%dT%H:%M:%OS")
>> [1] "1995-05-25T15:30:00"
>>> strftime(t1, format = "%Y-%m-%dT%H:%M:%OS%z")
>> [1] "1995-05-25T15:30:00Mitteleuropäische Sommerzeit"
>>> # Ends in "Mitteleuropäische Sommerzeit", not in +10:00, so time  
>>> zone is ignored!
>>> # Also no difference beetween %z and %z !
>>> strftime(t1, format = "%Y-%m-%dT%H:%M:%OS%Z")
>> [1] "1995-05-25T15:30:00Mitteleuropäische Sommerzeit"
>>> # All this does NOT remove the "Mitteleuropäische Zeit" from the  
>>> strftime output!!
>>>
>>> # Can locale solve the problem?
>>> Sys.getlocale(category = "LC_TIME")
>> [1] "German_Germany.1252"
>>> Sys.setlocale("LC_TIME", "English")
>> [1] "English_United States.1252"
>>>
>>> strftime(t1, format = "%Y-%m-%dT%H:%M:%OS%z")
>> [1] "1995-05-25T15:30:00Mitteleuropäische Sommerzeit"
>>> # [1] "1995-05-25T15:30:00Mitteleuropäische Sommerzeit" -- No  
>>> change.
>>>
>>> # does t1 actually have time zone?
>>> attributes(t1)
>> $names
>> [1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"   
>> "isdst"
>>
>> $class
>> [1] "POSIXlt" "POSIXt"
>>
>>>
>>> format(t1, format = "%Y-%m-%dT%H:%M:%OS%z") # usetz = TRUE) # no  
>>> change on usetz
>> [1] "1995-05-25T15:30:00Mitteleuropäische Sommerzeit"
>>>
>>> # Is the : in offset the problem?
>>> t3 <- strptime("1995-05-25T15:30:00+1000", format = "%Y-%m-%dT%H: 
>>> %M:%S%z")
>>> attributes(t3)
>> $names
>> [1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"   
>> "isdst"
>>
>> $class
>> [1] "POSIXlt" "POSIXt"
>>
>>> format(t3, format = "%Y-%m-%dT%H:%M:%OS%z")
>> [1] "1995-05-25T07:30:00Mitteleuropäische Sommerzeit"
>>> # [1] "1995-05-25T07:30:00Mitteleuropäische Sommerzeit"
>>>
>>> strftime(t1, format = "%Y-%m-%dT%H:%M:%OS%z", tz = "+0200") # no  
>>> effect on setting tz
>> [1] "1995-05-25T15:30:00Mitteleuropäische Sommerzeit"
>>>
>>> Sys.setenv(TZ="GMT") # no working effect on format and strftime
>>
> -- 
>
> David Winsemius, MD
> West Hartford, CT
>
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David Winsemius, MD
West Hartford, CT