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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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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-- Rich FitzJohn rich.fitzjohn <at> gmail.com | http://homepages.paradise.net.nz/richa183 You are in a maze of twisty little functions, all alike
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-- Brian D. Ripley, [EMAIL PROTECTED] 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
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