RE: [R] time zones, daylight saving etc.

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Fri 13 May 2005 - 07:11:27 EST

On Thu, 12 May 2005, Prof Brian Ripley wrote:

> Yes, I did mention the OS was unstated, knowing that some had problems. I
> will try to investigate why this is not working on Windows for a future
> release.

For the record, this is a POSIX-compliance failure. The POSIX standard says

   Local timezone information is used as though localtime() calls tzset()

but Windows requires tzset() to be called explicitly.

I've added a workaround in R-patched.

>
> For Windows users something like
>
> .../RGui.exe TZ=GMT
>
> should do it.
>
> On Thu, 12 May 2005, Vadim Ogranovich wrote:
>
>> Works for me on Linux:
>>> Sys.time()
>> [1] "2005-05-12 10:22:31 PDT"
>>> Sys.putenv(TZ="GMT")
>>> Sys.time()
>> [1] "2005-05-12 17:22:37 GMT"
>>
>> I extensively use the reset of TZ to parse times.
>>
>>> -----Original Message-----
>>> From: r-help-bounces@stat.math.ethz.ch
>>> [mailto:r-help-bounces@stat.math.ethz.ch] On Behalf Of Gabor
>>> Grothendieck
>>> Sent: Thursday, May 12, 2005 6:18 AM
>>> To: Prof Brian Ripley
>>> Cc: Carla Meurk; r-help@stat.math.ethz.ch
>>> Subject: Re: [R] time zones, daylight saving etc.
>>>
>>> I have tried this but on Windows XP R 2.1.0 found I had to
>>> set it outside of R prior to starting R.
>>>
>>> 1. unsuccessful
>>>
>>>> Sys.time()
>>> [1] "2005-05-12 09:08:03 Eastern Daylight Time"
>>>> Sys.putenv(TZ="GMT")
>>>> Sys.time() # no change
>>> [1] "2005-05-12 09:08:12 Eastern Daylight Time"
>>>
>>> 2. OK
>>>
>>> C:\>set tz=GMT
>>>
>>> C:\>start "" "\Program Files\R\rw2010\bin\r.exe"
>>>
>>> R : Copyright 2005, The R Foundation for Statistical
>>> Computing Version 2.1.0 Patched (2005-04-18), ISBN 3-900051-07-0
>>>
>>> R is free software and comes with ABSOLUTELY NO WARRANTY.
>>> You are welcome to redistribute it under certain conditions.
>>> Type 'license()' or 'licence()' for distribution details.
>>>
>>> Natural language support but running in an English locale
>>>
>>> R is a collaborative project with many contributors.
>>> Type 'contributors()' for more information and 'citation()'
>>> on how to cite R or R packages in publications.
>>>
>>> Type 'demo()' for some demos, 'help()' for on-line help, or
>>> 'help.start()' for a HTML browser interface to help.
>>> Type 'q()' to quit R.
>>>
>>>> Sys.time()
>>> [1] "2005-05-12 13:10:58 GMT"
>>>
>>> I assume it could be set in .Renviron but it would be nice if
>>> one could set it right from within R so that one can write a
>>> function that sets it, does processing and then sets it back.
>>> Don't know if this is possible.
>>>
>>> On 5/12/05, Prof Brian Ripley <ripley@stats.ox.ac.uk> wrote:
>>>> Would it not just be easier to set the timezone to GMT for the
>>>> duration of the calculations? I don't see an OS mentioned
>>> here, but
>>>> on most TZ=GMT for the session will do it.
>>>>
>>>> On Thu, 12 May 2005, Rich FitzJohn wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> seq.dates() in the chron package does not allow creating
>>> sequences
>>>>> by minutes, so you'd have to roll your own sequence generator.
>>>>>
>>>>> Looks like the tzone attribute of the times is lost when using
>>>>> min(),
>>>>> max() and seq(). You can apply it back manually, but it does not
>>>>> affect the calculation, since POSIXct times are stored as seconds
>>>>> since 1/1/1970 (?DateTimeClasses).
>>>>>
>>>>> ## These dates/times just span the move from NZDT to NZST:
>>>>> dt.dates <- paste(rep(15:16, c(5,7)), "03", "2003", sep="/")
>>>>> dt.times <- paste(c(19:23, 0:6), "05", sep=":") dt <-
>>>>> paste(dt.dates, dt.times)
>>>>>
>>>>> ## No shift in times, or worrying about daylight savings;
>>>>> appropriate ## iff the device doing the recording was not itself
>>>>> adjusting for ## daylight savings, presumably.
>>>>> datetime <- as.POSIXct(strptime(dt, "%d/%m/%Y %H:%M"), "GMT")
>>>>>
>>>>> ## Create two objects with all the times in your range,
>>> one with the
>>>>> ## tzone attribute set back to GMT (to match datetimes),
>>> and one ##
>>>>> without this.
>>>>> mindata1 <- mindata2 <- seq(from=min(datetime), to=max(datetime),
>>>>> by="mins") attr(mindata2, "tzone") <-
>>>>> "GMT"
>>>>>
>>>>> fmt <- "%Y %m %d %H %M"
>>>>> ## These both do the matching correctly:
>>>>> match(format(datetime, fmt), format(mindata1, fmt, tz="GMT"))
>>>>> match(format(datetime, fmt), format(mindata2, fmt, tz="GMT"))
>>>>>
>>>>> ## However, the first of these will not, as it gets the
>>> timezone all
>>>>> ## wrong, since it's neither specified in the call to
>>> format(), or
>>>>> as ## an attribute of the POSIXct object.
>>>>> match(format(datetime, fmt), format(mindata1, fmt))
>>>>> match(format(datetime, fmt), format(mindata2, fmt))
>>>>>
>>>>> ## It is also possible to run match() directly off the POSIXct
>>>>> object, ## but I'm not sure how this will interact with
>>> things like
>>>>> leap ## seconds:
>>>>> match(datetime, mindata1)
>>>>>
>>>>> Time zones do my head in, so you probably want to check this all
>>>>> pretty carefully. Looks like there's lots of gotchas (e.g.
>>>>> subsetting a POSIXct object strips the tzone attribute).
>>>>>
>>>>> Cheers,
>>>>> Rich
>>>>>
>>>>> On 5/12/05, Gabor Grothendieck <ggrothendieck@gmail.com> wrote:
>>>>>> You could use the chron package. It represents date
>>> times without
>>>>>> using time zones so you can't have this sort of problem.
>>>>>>
>>>>>> On 5/10/05, Carla Meurk <ksm32@student.canterbury.ac.nz> wrote:
>>>>>>> Hi, I have a whole bunch of data, which looks like:
>>>>>>>
>>>>>>> 15/03/2003 10:20 1
>>>>>>> 15/03/2003 10:21 0
>>>>>>> 15/03/2003 12:02 0
>>>>>>> 16/03/2003 06:10 0
>>>>>>> 16/03/2003 06:20 0.5
>>>>>>> 16/03/2003 06:30 0
>>>>>>> 16/03/2003 06:40 0
>>>>>>> 16/03/2003 06:50 0
>>>>>>>
>>>>>>> 18/03/2003 20:10 0.5
>>>>>>> etc. (times given on a 24 hour clock)
>>>>>>>
>>>>>>> and goes on for years. I have some code:
>>>>>>>
>>>>>>> data<-read.table("H:/rainfall_data.txt",h=T)
>>>>>>> library(survival)
>>>>>>> datetime <- as.POSIXct(strptime(paste(data$V1,
>>> data$V2), "%d/%m/%Y
>>>>>>> %H:%M"), tz="NZST")
>>>>>>>
>>>>>>> which produces:
>>>>>>>
>>>>>>> [10] "2003-03-13 21:13:00 New Zealand Daylight Time"
>>>>>>> [11] "2003-03-15 13:20:00 New Zealand Daylight Time"
>>>>>>> [12] "2003-03-15 22:20:00 New Zealand Daylight Time"
>>>>>>> [13] "2003-03-15 22:21:00 New Zealand Daylight Time"
>>>>>>> [14] "2003-03-16 00:02:00 New Zealand Daylight Time"
>>>>>>> [15] "2003-03-16 18:10:00 New Zealand Standard Time"
>>>>>>> [16] "2003-03-16 18:20:00 New Zealand Standard Time"
>>>>>>> [17] "2003-03-16 18:30:00 New Zealand Standard Time"
>>>>>>>
>>>>>>> My problem is that "15/03/2003 12:02" has become
>>> "16/03/2003 00:02"
>>>>>>> i.e. it is 12 hours behind (as is everything else),
>>> but also, I
>>>>>>> do not want to change time zones.
>>>>>>>
>>>>>>> The 12 hour delay is not really a problem just an
>>> annoyance, but
>>>>>>> the time zone change is a problem because later on I
>>> need to match
>>>>>>> up data by time using
>>>>>>>
>>>>>>> mindata<-seq(from=min(datetime),to=max(datetime),by="mins")
>>>>>>> newdata<-matrix(0,length(mindata),1)
>>>>>>> newdata[match(format.POSIXct(datetime,"%Y %m %d %H
>>>>>>> %M"),format.POSIXct(mindata,"%Y %m %d %H %M"))]<-data$V3
>>>>>>>
>>>>>>> and things go wrong here with matching repeating times/missing
>>>>>>> times around the timezone changes and, my resulting vector is 1
>>>>>>> hour shorter than my other series. From the R help I
>>> see that my
>>>>>>> OS may be to blame but, even if I specify tz="GMT" I still get
>>>>>>> NZST and NZDT. Can someone help?
>>>>>>>
>>>>>>> I hope this all makes sense
>>>>>>>
>>>>>>> Carla
>>>>>>>
>>>>>>> ______________________________________________
>>>>>>> R-help@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
>>>>>>>
>>>>>>
>>>>>> ______________________________________________
>>>>>> R-help@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
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Rich FitzJohn
>>>>> rich.fitzjohn <at> gmail.com |
>>> http://homepages.paradise.net.nz/richa183
>>>>> You are in a maze of twisty little
>>> functions,
>>>>> all alike
>>>>>
>>>>> ______________________________________________
>>>>> R-help@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
>>>>>
>>>>
>>>> --
>>>> Brian D. Ripley, ripley@stats.ox.ac.uk
>>>> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
>>>> University of Oxford, Tel: +44 1865 272861 (self)
>>>> 1 South Parks Road, +44 1865 272866 (PA)
>>>> Oxford OX1 3TG, UK Fax: +44 1865 272595
>>>>
>>>> ______________________________________________
>>>> R-help@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
>>>>
>>>
>>> ______________________________________________
>>> R-help@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
>>>
>>
>>
>
> --
> Brian D. Ripley, ripley@stats.ox.ac.uk
> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
> University of Oxford, Tel: +44 1865 272861 (self)
> 1 South Parks Road, +44 1865 272866 (PA)
> Oxford OX1 3TG, UK Fax: +44 1865 272595
>
> ______________________________________________
> R-help@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
>

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Fri May 13 07:15:25 2005

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