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

From: David Winsemius <dwinsemius_at_comcast.net>
Date: Fri, 11 Mar 2011 09:15:08 -0500

On Mar 11, 2011, at 8:54 AM, Daniel Nüst wrote:

> 2011/3/11 David Winsemius <dwinsemius@comcast.net>:

>> On Mar 10, 2011, at 8:46 PM, David Winsemius wrote:
>>> On Mar 10, 2011, at 11:17 AM, Daniel Nüst wrote:
>>>> 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"
>

> This procudes the same output on my machine, but still does not solve
> the problem, which lies on the output side, sorry if I was not clear
> about that before:
>

> time <- 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")
> format(x = time, format = "%Y-%m-%d %H:%M:%S%z")
> # [1] "1995-05-26 01:30:00Mitteleuropäische Zeit"
> strftime(x = time, format = "%Y-%m-%d %H:%M:%S%z")
> # [1] "1995-05-26 03:30:00Mitteleuropäische Sommerzeit"
>

> But I need "...01:30:00+01:00", or "...01:30:00+0100", as I expect
> from %z because in ?strptime I read:
>

> "%z
> Signed offset in hours and minutes from UTC, so -0800 is 8 hours
> behind UTC."
>

> and
>

> "Note that when %z or %Z is used for output with an object with an
> assigned timezone an attempt is made to use the values for that
> timezone — but it is not guaranteed to succeed."
>

> Does this just mean it just won't work?
>

> Let me rephrase my question: How can I create a time object from the
> character string "1995-05-25T15:30:00-10:00" and get exactly the same
> character string again when formatting it/printing it?

 > x <- 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")  > x
[1] "1995-05-26 01:30:00 GMT"
 > format(x, "%Y-%m-%d %H:%M:%S%z")
[1] "1995-05-26 01:30:00+0000"
 > format(x, "%Y-%m-%dT%H:%M:%S%z")
[1] "1995-05-26T01:30:00+0000"

It is easy todeal with the "T" separator. You did say that the ":" was optional in the output, didn't you?

-- 
David.
>

> Thanks for any help!
> /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 >>> >>> ______________________________________________ >>> R-help_at_r-project.org mailing list >>> https://stat.ethz.ch/mailman/listinfo/r-help >>> PLEASE do read the posting guide >>> http://www.R-project.org/posting-guide.html >>> and provide commented, minimal, self-contained, reproducible code. >> >> David Winsemius, MD >> West Hartford, CT >> >> >
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD West Hartford, CT ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Received on Fri 11 Mar 2011 - 14:21:22 GMT

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