[R] time zones, daylight saving etc.

[Gabor Grothendieck]

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
> 
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