[R] Lattice: How to color the data points in splom() according to the panel they are plotted?

[Deepayan Sarkar]

On Mon, Jun 14, 2010 at 6:24 PM, Martin Maechler
<maechler at stat.math.ethz.ch> wrote:
> Dear Deepayan,
>
> this is in reply to a message almost 6 months ago :
>
>>>>>> Deepayan Sarkar <deepayan.sarkar at gmail.com>

[...]

>    > Thanks, I was going to say the same thing, except that it would be
> (1)
>    > conceptually simpler just to add the 'i' and 'j' values as arguments
>    > to the "panel" function (the 'pargs' variable). The colors could then
>    > be passed through as part of the ... arguments, and the relevant entry
>    > extracted in the panel function.
> (2)
>    > The other option is to keep a global counter and increment it inside
>    > the panel function, and choosing colors based on that counter and
>    > knowledge of the order in which panels are drawn. Not very elegant,
>    > but the least intrusive solution I can think of.
>
>    > -Deepayan
>
> Against the R-forge version of lattice,
> the following very small patch to  panel.pairs
> would allow users to use '(1)' i.e., provide  panel functions
> with (i,j) arguments directly.
> I'm pretty sure that the change could not easily break existing
> splom() usage.
>
> --- R/splom.R   (revision 619)
> +++ R/splom.R   (working copy)
> @@ -291,7 +291,8 @@
>                                    y = z[subscripts, i]),
>  ##                                    panel.number = panel.number,
>  ##                                    packet.number = packet.number),
> -                              list(...))
> +                              list(...),
> +                              list(i = i, j = j))
>                         else
>                             c(list(x = z[subscripts, j],
>                                    y = z[subscripts, i],
> @@ -299,7 +300,8 @@
>                                    subscripts = subscripts),
>  ##                                    panel.number = panel.number,
>  ##                                    packet.number = packet.number),
> -                              list(...))
> +                              list(...),
> +                              list(i = i, j = j))
>
>                     if (!("..." %in% names(formals(panel))))
>                         pargs <- pargs[intersect(names(pargs), names(formals(panel)))]

Done in r-forge svn.

-Deepayan

>
>
> With the above change,
> a user could use a panel function with (i,j) arguments,
> and e.g. say
>
> Cmat <- outer(1:6,1:6,
>              function(i,j) rainbow(11, start=.12, end=.5)[i+j-1])
>
> splom(~diag(6), ## for testing: superpanel=mypanel.pairs,
>      panel=function(x,y,i,j,...){
>               panel.fill(Cmat[i,j]); panel.splom(x,y,...)
>               panel.text(.5,.5, paste("(",i,",",j,")",sep=""))
>      })
>
>
> I think that would allow quite a bit more flexibility without
> the need to explicitly "hack"  panel.pairs
> (and having to maintain such a hack against the ever-enhancing
> lattice).
>
> Martin Maechler, ETH Zurich
>