[R] finer control of scales in xyplot

[Benjamin Tyner]

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.

Thanks,
Ben