[R] time zones, daylight saving etc.

[Carla Meurk]

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