-----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
[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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Type 'license()' or 'licence()' for distribution details.
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[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
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
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,
## tzone attribute set back to GMT (to match datetimes),
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
## wrong, since it's neither specified in the call to
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
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
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$V1,
%H:%M"), tz="NZST")
which produces:
[10] "2003-03-13 21:13:00 New Zealand Daylight Time"
[11] "2003-03-15 13:20:00 New Zealand Daylight Time"
[12] "2003-03-15 22:20:00 New Zealand Daylight Time"
[13] "2003-03-15 22:21:00 New Zealand Daylight Time"
[14] "2003-03-16 00:02:00 New Zealand Daylight Time"
[15] "2003-03-16 18:10:00 New Zealand Standard Time"
[16] "2003-03-16 18:20:00 New Zealand Standard Time"
[17] "2003-03-16 18:30:00 New Zealand Standard Time"
My problem is that "15/03/2003 12:02" has become
i.e. it is 12 hours behind (as is everything else),
do not want to change time zones.
The 12 hour delay is not really a problem just an
the time zone change is a problem because later on I
up data by time using
mindata<-seq(from=min(datetime),to=max(datetime),by="mins")
newdata<-matrix(0,length(mindata),1)
newdata[match(format.POSIXct(datetime,"%Y %m %d %H
%M"),format.POSIXct(mindata,"%Y %m %d %H %M"))]<-data$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
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