[R] lattice key inside panel

[Deepayan Sarkar]

On Wed, Feb 4, 2009 at 8:21 AM, Iago Mosqueira <iago.mosqueira at gmail.com> wrote:
> Hello,
>
> I am trying to draw a key inside a single panel in a lattice xyplot. The
> panel function uses panel.number() to use a slightly different style for
> one of the panels. Once inside than panel I am using
>
> draw.key(list(text=list(lab='catch'),
>          lines=list(lwd=c(2)),
>          text=list(lab='landings'),
>          rectangles=list(col=rgb(0.1, 0.1, 0, 0.1)),
>         x=0, y=1, corner=c(0,0)), draw=TRUE)
>
> which gets me the key right in the middle of the panel. I would like to
> have at the top or bottom. Changes to the values of x, y or corner do
> not seem to change the position at all.
>
> lattice.getOption("legend.bbox") returns 'panel'.
>
> I am quit sure I am missing something essential, but can this be done
> without calling directly grid methods?

No. The placement controls such as x, y, and corner are not handled by
draw.key itself, but rather by the high-level plotting function. Used
directly, draw.key() basically gives you a low-level grid "grob", and
you need to use grid tools to do anything with them ('draw=TRUE'
simply calls grid.draw() on the grob before returning it). The
simplest way to change position is to supply a simple 'vp' argument.

xyplot(1~1,
       panel = function(...) {
           require(grid)
           panel.xyplot(...)
           draw.key(list(text=list(lab='catch'),
                         lines=list(lwd=c(2)),
                         text=list(lab='landings'),
                         rectangles=list(col=rgb(0.1, 0.1, 0, 0.1))),
                    draw = TRUE,
                    vp = viewport(x = unit(0.75, "npc"), y = unit(0.9, "npc")))
       })

 More complex positioning (perhaps depending on the size of the
legend) will need more work.

-Deepayan