Read the help desk article in R News 4/1.
On 9/14/06, Richard Evans <revans at jlab.org>
wrote:> Dear R-forum,
>
> I am looking for a good resource/help on working with POSIXct values and
> controlling the pretty x-axis labels and tick marks for a data VS time
> plots. Specifically, I wish to do programming logic which creates
> different vertical ablines calculations based on the range of times
> which i am working on. The default plot results are adequate, but I
> would love to make explicit calls on how the x-axis annotates the
> timestamps.
>
> Does anyone have example code or know of a good reference for these
> kinds of R-programming tasks?
>
>
> Here's a simplified example:
> ----------------------------------------------------------
> I have a large data set that consists of N pairs of values and
> timestamps strings.
> Like this:
>
> TheData <- c(1.2, 0.9, etc...[to the Nth
> datapoint])
> TheTime <- c("9/1/2006 8:00", "9/1/2006 8:13",
etc...[to the Nth
> timestamp])
>
> I convert the timestamp strings into POSIXct types as:
>
> TheTime <- as.POSIXct(strptime(TheTime, format="%m/%d/%Y
%H:%M"))
>
> And create a plot as such:
>
> plot(MyTime,MyData)
>
> ----------------------------------------------------------
>
> And here is a specific question:
>
> How do I calculate the number of months than are spanned between two
> POSIXct values?
> (i.e. NumOfMonths <- MonthFunction(range(MyTimeStampData))
>
> Thanks-in-advance,
> - rich
>
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