legend idea for latticeExtra

Dear list,


 I've written a small utility function to add arbitrary legend(s) to a
lattice graph (or a combination of them), much like the legend function of
base graphics. I though perhaps it could be useful to someone else, or
improved by suggestions. I understand this goes against the lattice paradigm
somewhat, in that you short-cut the link between group variables and the
appearance of the legend. There are some cases where I was missing this kind
of raw command, though, and the custom legend dendrogram of the lattice book
is intimidating if not a bit overkill.

 llegend <- function(x=0.5, y=0.5, loc=FALSE, text=c("a", "b"), unit="npc",
                                        pch=1, lty=NULL,
col=seq_along(text), cex=0.6, cex.title=0.8,  ...){
        if(loc) {
                ll <- grid.locator(unit)
                print(ll)
                x <- as.numeric(ll$x)
                y <- as.numeric(ll$y)
                }
 lines <- !is.null(lty)
 points <- !is.null(pch)

        keyGrob <- draw.key(key=simpleKey(text, lines=lines,
                                                        points =
points,cex=cex, cex.title=cex.title, ...),
                                                vp=viewport(x=unit(x, unit),
y=unit(y, unit)), draw=F)
        grid.draw(keyGrob)
        invisible(keyGrob)
 }

 # example (locator used for the second legend)
 xyplot(1~1)
 llegend()
 llegend(loc=T, title="Here goes another") # click wherever on the viewport.


 Best wishes,

 baptiste