R help - Oct 2003 - How to use panel.qqmathline?

Dear R users:

How can I use panel.qqmathline, in package lattice, to add
straight lines onto the plots generated by qqmath?
I read help pages of qqmath, panel.qqmathline, xyplot, ...,
but just can't one example that shows how to make it work.

For example, 
> data(sleep)
> qqnorm(~ extra | group, data=sleep, aspect=1)
how can I use panel.qqmathline?

Thanks very much for your help,

Joseph Lu
Department of Statistics
National Cheng-Kung University
Tainan, Taiwan

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At 19:52 2003-10-04 +0800, you wrote:
>How can I use panel.qqmathline, in package lattice, to add
>straight lines onto the plots generated by qqmath?
>[...]
> > data(sleep)
> > qqnorm(~ extra | group, data=sleep, aspect=1)
Try

qqmath(~ extra | group,  data = sleep, aspect = 1,
             distribution = qnorm, prepanel = prepanel.qqmathline,
             panel = function(x, y, ...)  {
               panel.qqmathline(y, distribution = qnorm, ...)
               panel.qqmath(x, y, ...)
             })

Hope this helps,
Henric

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