[R] time zones, daylight saving etc.

From: Carla Meurk <ksm32_at_student.canterbury.ac.nz>
Date: Wed 11 May 2005 - 13:28:57 EST


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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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed May 11 13:37:11 2005

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