What if I have a time series which is collected every Monday, please?
What is the proper way to use the start option within the ts command in order to indicate that this is Monday data, please?
ts objects don't directly support dates. There is some provision for monthly data, but this isn't the same as uniform, across-the-board date support. What they do have is a start time, a deltat, and frequency (observations per period). The main reason to use ts objects *isn't* the date/time handling, but for the nice functions (acf, spectrum, etc) you can use for regularly spaces time samples.
For weekly data, I'd use one of the following approaches (assuming the series starts in the first Monday of 2003):
1) # dates in a year,week format > foo <- ts(1:100,start=c(2003,1),frequency=52)
or
2)
# dates as numeric representation of POSIXct objects
foo <- ts(1:100,start=as.numeric(as.POSIXct("2003-1-6")),deltat=60*60*24*7)
> start(foo)
[1] 1041764400
> end(foo)
[1] 1101639600
> last <- end(foo)
> class(last) <- "POSIXct"
> last
[1] "2004-11-29 New Zealand Daylight Time"(2) depends on as.numeric(POSIXct.object) giving a sensible, single-digit answer. This is not guaranteed. It works today, but nobody promised this approach would work tomorrow.
Hope that helps.
Cheers
Jason -- Indigo Industrial Controls Ltd. http://www.indigoindustrial.co.nz 64-21-343-545 [EMAIL PROTECTED]
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