[R] Problem with llines in lattice

[Deepayan Sarkar]

On 10/29/05, John Fox <jfox at mcmaster.ca> wrote:
> Dear r-help list members,
>
> I'm experiencing problems getting type="b" (or "o" or "c") to work in
> llines(). Try, e.g., the following scaled-down example:
>
> x <- factor(c("a", "b", "a", "b"))
> y <- c(1,2,1,2)
> z <- factor(c("A", "A", "B", "B"))
> symbols <- 1:2
> lines <- 1:2
> colors <- 1:2
> zvals <- levels(z)
> xyplot(y~x|z, panel = function(x, y, subscripts, ...) {
>     for (i in 1:length(zvals)) {
>         sub <- z[subscripts] == zvals[i]
>         llines(x[sub], y[sub], lwd = 2, type = "b",
>           col = colors[i], pch = symbols[i], lty = lines[i])
>         }
>     })
>
> Only the lines (properly coloured with correct line types) appear, but no
> symbols are plotted.

It's bug in lplot.xy. Fortunately, panel.xyplot will do the same
thing, so you can use it instead of llines.

One comment: I'm not sure if this would work in your real application,
but for your toy example a more direct approach would be

xyplot(y ~ x | z, type = 'b', groups = z,
       col = colors, pch = symbols, lty = lines,
       lwd = 2)

-Deepayan