[R] Reversed but positive axis in trellis plots?

[Deepayan Sarkar]

On 3/5/08, Fredrik Karlsson <dargosch at gmail.com> wrote:
> Hi,
>
>  In my discpipline, it is common to plot one acoustic property on a
>  positive scale but from top to bottom on the ordinate and the same for
>  another measurement on the abscissa.
>  So, the origin of the plot is on the top right of the plot, with
>  increasing values to the left /down. This is to highlight the
>  correlation between the acoustic measurement and the position of the
>  forming structure, for instance when teaching it to students.
>
>  The grouping ability of the trellis plot is quite handy whan plotting
>  many instances of the same thing, so I was wondering if it is possible
>  to make a trellis xyplot behave this way?
>  Converting all values to negative and changing labels to the negative
>  of the negative seems one solution to the reverseness of the axes, but
>  how do I change the position? Is it possible?

You can always specify explicit limits that are reversed, e.g.,
ylim=c(100, 0). If you want this as a general behaviour but don't know
your data's range beforehand, one option might have been

    prepanel = function(x, y, ...) {
        list(ylim = rev(range(y)))
    }

Unfortunately, this doesn't work when relation="same", as the step of
combining the per-panel limits to obtain a common range disregards the
order.

-Deepayan