R help - Apr 2008 - identical scales per panel with relation="free"

Using xyplot, I am plotting observed versus predicted values conditional to the
values of a third variable.
I would thus like to have an aspect ratio of 1 and the same axis range.
Since the range of the values differs substantially between panels, the axis
ranges shall be different for each panel (along the lines of
relation="free"). However, x- and y-limits shall still be the same for
a given panel.
Any ideas on how to achieve that?

# Example (that produces different x/y-limits per panel)
set.seed(3484)
x <- data.frame(
    "x"=c(rnorm(10), rnorm(10, 10))
)
x$y <- x$x + rnorm(length(x$x))
x$z <- c(rep(c("A", "B"), c(10, 10)))

print(xyplot(y ~ x | z, data=x,
    aspect=1,
    scales=list(
        relation="free"
    ),
    panel=function(x, y, ...)
    {
        panel.abline(0, 1)
        panel.xyplot(x, y, ...)
    }
))

On 4/16/08, Andreas Krause <andreas at elmo.ch>
wrote:
>
>  Using xyplot, I am plotting observed versus predicted values conditional
to the values of a third variable.
>  I would thus like to have an aspect ratio of 1 and the same axis range.
>  Since the range of the values differs substantially between panels, the
axis ranges shall be different for each panel (along the lines of
relation="free"). However, x- and y-limits shall still be the same for
a given panel.
>  Any ideas on how to achieve that?
>
>  # Example (that produces different x/y-limits per panel)
>  set.seed(3484)
>  x <- data.frame(
>     "x"=c(rnorm(10), rnorm(10, 10))
>  )
>  x$y <- x$x + rnorm(length(x$x))
>  x$z <- c(rep(c("A", "B"), c(10, 10)))
>
>  print(xyplot(y ~ x | z, data=x,
>     aspect=1,
>     scales=list(
>         relation="free"
>     ),
>     panel=function(x, y, ...)
>     {
>         panel.abline(0, 1)
>         panel.xyplot(x, y, ...)
>     }
>  ))
Try this:

print(xyplot(y ~ x | z, data=x,
   aspect=1,
   scales=list(
       relation="free"
   ),
   prepanel = function(x, y, ...) {
       r <- range(x, y, ...)
       list(xlim = r, ylim = r)
   },
   panel=function(x, y, ...)
   {
       panel.abline(0, 1)
       panel.xyplot(x, y, ...)
   }
))

-Deepayan