[R] Annotate a levelplot (using abline) - Difficulty with trellis.

[Dan Bolser]

Hi,

I am generating a beautiful plot with the 'levelplot' function over my
square matrix of data. In order to help visualise the data I would
like to draw a diagonal line on the matrix. Because the plot is
actually a trellis object, I am having difficulty working out how to
do this. I have been reading around, but I don't see any easy solution
to the problem. (Most of the docs I have found are not of the type
'how to do it' but more like 'how to grok it'). After spending 1+ hour
reading and trying various things I figure its time to ask some people
who know ;-)

So far I have the following (which almost works!)...

    levelplot(
                our.data,
                plot.xy = (abline(0,1,col="white"))
                )

However the coordinate system / plot area being used are clearly not
those of the square matrix. I guess I should point out that the axes
of 'our.data' (the row and column names of the square matrix) are
ordered categories of the form;

    seq(2,9,0.5)


Thanks for any help !

Dan.