[R] time zones, daylight saving etc.
Vadim Ogranovich
vograno at evafunds.com
Thu May 12 19:23:25 CEST 2005
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 at stat.math.ethz.ch
> [mailto:r-help-bounces at 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 at 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"
>
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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 at 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 at 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 at 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 at 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 at 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 at 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 at 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 at 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
> >
>
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