[R] factors as bwplot x axis

[James Rome]

Dear List,

I am having problems getting my box and whisker plots to put boxes on
the right x-axis values.
x is the hour of the day from 0 to 23.
> unique(mdf$OnHour)
 [1]  5  4  6  7 11 12  9  8 19 14 13 21 20 10 18 17 15 16 23 22  0  1  3  2
mdf$OnHFact = factor(mdf$OnHour, levels=seq(0,23),
labels=as.character(seq(0,23)), exclude=NULL, ordered=TRUE)

I know there are data points for OnHFact=="0", but they do not appear on
the plot. The other data seem to be at their correct locations.
        hrs = seq(0, 23, 1)                
        hrlabs = as.character(seq(0,23,1))                   
        g = bwplot((gdf$tt)~gdf$OnHFact | gdf$Runway, data=gdf,
ylab="Taxi time (min)",
            main=title, xlab="Hour of day", 
par.strip.text=list(cex=0.7), rot=90,  #xlim=c(0, 24),
            scales=list(x = list(rot=90, cex=.6, at=hrs, labels=hrlabs )),
            panel = function(x, ...) {
                panel.grid(h = -1, v = -1)                           
                               
                panel.bwplot(x, ...)                                   
                                                                       
                                                                       
                   
          } )
                                               
        print(g)

Is there a prohibition of having a factor with a level of 0? If so, how
do I get around this?

I was also surprised that if I replace gdf$OnHFact by gdf$OnHour
(integers) in the above bwplot call, the plot flips and I get horizontal
whiskers of OnHour values for different tts.

So I am confused, and hope you kind people can help. I attach the zipped
dput gdf file

Thanks,
Jim Rome