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

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Fri 13 May 2005 - 03:27:01 EST

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 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
>>
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>> Type 'license()' or 'licence()' for distribution details.
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>> Natural language support but running in an English locale
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>>
>>> 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!
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>>
>
>

-- 
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 03:35:17 2005

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