On Tuesday 16 September 2003 22:00, Charles H. Franklin wrote:
> xyplot doesn't seem to want to label my x-axis with dates but instead puts
> the day-number for each date.
>
> begdate is the number of days since January 1, 1960 and was initially
> created by
>
> library(date)
>
> ...
>
> polls$begdate<-mdy.date(begmm,begdd,begyy)
>
> I create a new dataframe (pollstack) which includes begdate. In the process
>
> begdate seems to lose its date attribute so I redo it as:
> > pollstack$begdate<-as.date(pollstack$begdate)
>
> after which
>
> > attach(pollstack)
> > summary(pollstack)
>
> begdate pct names
> First :15Nov2002 Min. : 0.000 Clark : 54
> Last :10Sep2003 1st Qu.: 2.000 Dean : 54
> Median : 5.000 Edwards : 54
> Mean : 6.991 Gephardt: 54
> 3rd Qu.:12.000 Graham : 54
> Max. :29.000 Kerry : 54
> (Other) :216
>
>
> And all seems well.
>
> But xyplot continues to use day number on the x-axis. My plots are created
> by
>
> print(xyplot(pct ~ begdate | names, pch=2, cex=.2,
> prepanel = function(x, y) prepanel.loess(x, y, span = 1),
> main="2004 Democratic Primary Race",
> xlab = "Date of Survey",
> ylab = "Percent Support",
> panel = function(x, y) {
> panel.grid(h=-1, v= -1)
> panel.xyplot(x, y, pch=1,col=2,cex=.7)
> panel.loess(x,y, span=.65, lwd=2,col=4)
> }, ) )
>
> What am I missing?
The fact that xyplot doesn't know anything about the "date" class. I'm not
familiar with the date package, but the docs and a few experiments seem to
indicate that an object of class "date" is simply a numeric/integer vector
with the class attribute set to "date". xyplot interprets it as plain numeric
data.
You may be able to get what you want by
print(xyplot(pct ~ factor(as.character(begdate)) | names, pch=2, cex=.2,
prepanel = function(x, y) prepanel.loess(x, y, span = 1),
...
(but this will try to label all unique dates, which may not be good).
Is the date class standard enough to warrant including a check for it in
lattice ?
Deepayan
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