[R] Lattice: splom plots for different factors with correlation in lower.panel

[Tom Porteus]

Hello list,
I am looking to create a figure for my dataset using splom, where there is a
splom subplot for each level of a factor within, for example, a 2x2 layout. 
For each subplot, I wish to put the r-value between each variable pair in
the lower panel.  The code I have thus far is below, using the iris dataset
so that it is reproducible.  This almost does what I want, but for some
reason overlays the r-values for each level in each subplot.

I think the problem is something to do with the lower.panel function call
within my custom function, but I am not a huge whizz using lattice and can't
figure out what it is.  If I put the panel.text call in the lower.panel
function, it only causes a similar problem.  Apologies if there is something
obvious I have missed, I hope there is someone out there who can help me!

var.cor <- list()
for(i in 1:3){
	var.cor[[i]] <- abs(cor(subset(iris[1:4], iris$Species ==
levels(iris$Species)[i])))	#calculate variable correlation for each species
	var.cor[[i]] <- data.frame(values = as.vector(var.cor[[i]]), row =
as.vector(row(var.cor[[i]])), col = as.vector(col(var.cor[[i]])))
	var.cor[[i]] <- subset(var.cor[[i]], col<row)	#create data frame with value
and row & col indexes for values with each panel
}
panel.pairs.cor <- function(z, ...){
	panel.pairs(z, upper.panel=panel.splom, lower.panel=function(){}, ...)
	for(i in 1:3){
		panel.text(x=var.cor[[i]]$row, y=var.cor[[i]]$col,
labels=round(var.cor[[i]]$values, 2))
	}	
}
splom(~iris[1:4]|iris$Species, layout=c(2,2), pscales=0, col="black",
xlab="", ylab="", as.table=TRUE, superpanel=panel.pairs.cor)

Many thanks,
Tom


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