[R] time zones, daylight saving etc.
Gabor Grothendieck
ggrothendieck at gmail.com
Thu May 12 15:17:36 CEST 2005
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 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
>
More information about the R-help
mailing list