You say median for each panel but tapply gets medians for each variety
(chartjunk IMHO). Regardless, *this case* has nothing to do with
panel.abline. Add print(median.values) to your panel function would have
hinted as to the missing piece.

# medians for each panel:
dotplot(variety ~ yield | site, data = barley,
       scales=list(x=list(log=TRUE)),
       layout = c(1,6),
       panel = function(x,y,...) {
       panel.dotplot(x,y,...)
       median.values <- median(x)
       panel.abline(v=median.values, col.line="red")
})

# medians for each variety
 dotplot(variety ~ yield | site, data = barley,
       scales=list(x=list(log=TRUE)),
       layout = c(1,6),
       panel = function(x,y,...) {
       panel.dotplot(x,y,...)
       median.values <- tapply(x, y, median)
panel.abline(v=median.values, col.line="red")
       }
       )

Cheers

On Wed, Jun 6, 2012 at 6:10 AM, maxbre <mbressan@arpa.veneto.it> wrote:

> by considering this example from barley dataset
>
> #code start
>
> dotplot(variety ~ yield | site, data = barley,
>        scales=list(x=list(log=TRUE)),
>        layout = c(1,6),
>        panel = function(...) {
>        panel.dotplot(...)
>        #median.values <- tapply(x, y, median)            # medians for each
> variety
>        #panel.abline(v=median.values, col.line="red")    # but this is not
> working!
>        #panel.curve(...)                                 # how to properly
> set this?
>        }
>        )
>
> #code end
>
> I want to plot as a reference vertical line the medians for each panel
>
> I’ve been reading in
> https://stat.ethz.ch/pipermail/r-help/2009-January/185384.html
> that it’s not possible with panel.abline() and it’s probably necessary to
> use panel.curve() instead; unfortunately I can’t figure (manage) how, any
> help for this?
>
> thank you
>
>
>
>
> --
> View this message in context:
> http://r.789695.n4.nabble.com/how-to-add-a-vertical-line-for-each-panel-in-a-lattice-dotplot-with-log-scale-tp4632513.html
> Sent from the R help mailing list archive at Nabble.com.
>
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> PLEASE do read the posting guide
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