[R] how to plot separate lm ablines on the same xyplot by group

[Bert Gunter]

Please read ?panel.superpose  again and pay attention to the
panel.groups argument, where this can be specified.

-- Bert

On Wed, Apr 18, 2012 at 12:34 PM, Louis Plough <lplough at usc.edu> wrote:
> Hi,
> I am trying to use xyplot to plot the relationship between size and day
> (y~x) by a food factor that has two levels, low and high. I have 3 reps per
> factor/day.  I want the plots from each food treatment on the same axiss,
> so I used this code:
>
> xyplot(Size ~ Day, groups = Food, data = louis.data.means,col=1,
> pch=c(1,17),
> panel=function(x,y,groups,...){
> panel.superpose(x,y,groups,...)
> tmp.lm<-lm(y~x)
> panel.abline(tmp.lm)
> panel.text(2, 250, label=format(tmp.lm$coefficients[2], digits=4), pos=4)
> }
> )
> This produces a graph of the two treatments (open circles for the low food
>  vs triangles for the high food) on the same plot, but only one regression
> line (and slope)  which seems to splits the difference between the two
> factors (treats them as the same data set).  I would like to produce a
> separate regression line for the data from each of the two factors (high
> food vs low food).
>
> Is there a way to subset the lm by the factor "food"?
>
> Louis
>
>        [[alternative HTML version deleted]]
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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