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

[David Winsemius]

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")
>
> 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