[R] Plotting curves in lattice panels

[Deepayan Sarkar]

On 9/18/08, David Scott <d.scott at auckland.ac.nz> wrote:
>
>  I have a data set concerning ferritin levels in blood. There are three
> relevant columns for this question, ferritin (continuous), score (ordered,
> from 0 to 8) and gender. There is a good linear relationship between
> log(ferritin) and score for each gender.
>
>  I can create a lattice plot on the log scale showing the data and the
> fitted line:
>  xyplot(log(ferritin)  ~ total|gender, data = blood,
>        panel = function(x, y, ...){
>          panel.xyplot(x, y)
>          panel.abline(lm(y ~ x), type = 'l', ...)
>        }
>  )
>
>  I would like to be able to plot the data and the fitted line on the
> original scale however. I can't see how to do that.

Something like this should work:

xyplot(ferritin  ~ total|gender, data = blood,
       panel = function(x, y, ...){
           panel.xyplot(x, y)
           fm <- lm(log(y) ~ x)
           panel.curve(exp(predict(fm, newdata = list(x = x))))
       })

-Deepayan