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

ilai keren at math.montana.edu
Wed Apr 18 23:11:10 CEST 2012

```On Wed, Apr 18, 2012 at 2:07 PM, Louis Plough <lplough at usc.edu> wrote:
> If you could lead me to an example with code, that would help me figure out
> how to do it for my function

The states example in ?xyplot uses groups and subscripts in a panel function

>> I read it, but I guess I don't quite understand which arguments to pass
>> panel.groups to get different lm objects based on the two groups within
>> Food.

You are confused. panel.superpose != panel.groups. You probably wanted
something like (and next time please provide data):

x <- rep(1:10,2)
y <- rnorm(20,rep(1:2,each=10)*x)
g <- gl(2,10)
xyplot(y~x,groups=g,
panel=panel.superpose, panel.groups=function(x,y,...){
tmp.lm<-lm(y~x)
panel.abline(tmp.lm)
panel.text(2, coef(tmp.lm)%*%c(1,2),
label=format(tmp.lm\$coefficients[2], digits=4), pos=4)
panel.xyplot(x,y,...)
})

HTH

>>
>> On Wed, Apr 18, 2012 at 3:44 PM, Bert Gunter <gunter.berton at gene.com>wrote:
>>
>>> 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]]
>>> >
>>> > ______________________________________________
>>> > R-help at r-project.org mailing list
>>> > https://stat.ethz.ch/mailman/listinfo/r-help
>>> http://www.R-project.org/posting-guide.html
>>> > and provide commented, minimal, self-contained, reproducible code.
>>>
>>>
>>>
>>> --
>>>
>>> Bert Gunter
>>> Genentech Nonclinical Biostatistics
>>>
>>> Internal Contact Info:
>>> Phone: 467-7374
>>> Website:
>>>
>>>
>>
>>
>
>        [[alternative HTML version deleted]]
>
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