Re: [R] finer control of scales in xyplot

From: Deepayan Sarkar <deepayan.sarkar_at_gmail.com>
Date: Tue 09 Jan 2007 - 01:53:53 GMT

On 1/8/07, Benjamin Tyner <btyner@stat.purdue.edu> wrote:
> When plotting over multiple pages in lattice, I'd like to be able to
> have "same" scales within a page, but "free" scales between pages. In
> other words, something like:
>
> z<-data.frame(x=1:100,
> y=runif(100),
> d=rep(1:2,50),
> p=rep(1:2,each=50))
>
> plot<-xyplot(y~x|d*p,
> data=z,
> scales=list(x=list(relation="free")),
> layout=c(1,2))
>
> but within a page, to have common x-axes. As long as 'x' is sorted, I
> can get the desired effect by transforming x to a relative scale:
>
> plot<-xyplot(y~unlist(with(z,tapply(x,p,function(x)
> (x-min(x))/diff(range(x)))))|d*p,
> data=z,
> layout=c(1,2))
>
> except that I'd like the tickmark labels to be in the original units of
> 'x'. I've started looking at xscale.components.default to see whether it
> can work on a per-page (instead of per-panel) basis, but I get the
> nagging suspicion that I'm making this harder than it needs to be. Any
> assistance greatly appreciated.

A "nice" solution is unlikely. As a general rule, the trellis object doesn't know anything about what layout it's going to be plotted with, and unfortunately the panel-specific scales are determined when the object is created, not when it is plotted (I don't remember all the reasons for this choice, but changing it would require a major overhaul). A similar task, row-specific or column-specific "free" scales, is difficult for the same reason.

If I need to do this, I usually have in scales

  1. relation="free"
  2. limits = list(lim1, lim2, ...) where lim1, lim2, etc are packet-specific limits (they have to be supplied explicitly). You can omit this if you can make sure your prepanel function gives you the right things.

This will almost do what you want, but will repeat the ticks/labels for every panel. To suppress that you can additionally have

3. at = list(TRUE, NULL, ...) etc where NULL means ticks/labels won't be drawn.

This doesn't really help, because the space will still be wasted, so finally,

4. add par.settings = list(layout.heights = list(axis.panel = c(1, 0, ...)))

-Deepayan



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