[R] How to overlay lines and rectangles in lattice plot key

[sbihorel]

Hi,

I would like to create a custom key for a lattice xyplot in which line 
elements are displayed on top of rectangle elements. In the example code 
below, the lines and rectangles are shown side by side (the legend 
itself is meaningless, but that is not the point). Is there a way to 
overlay these key elements (but not the text)?

Thanks

xyplot(Sepal.Length + Sepal.Width ~ Petal.Length + Petal.Width,
   iris,
   type = c("p", "r"),
   jitter.x = TRUE,
   jitter.y = TRUE,
   factor = 5,
   key = list(
     column=4,
     text=list(lab=letters[1:4]),
     lines=list(col=1:4, pch=1:4, type='b'),
     rectangles=list(col=1:4, alpha=0.25, border=FALSE)
   )
)