[R] user defined panel function

[Martin Henry H. Stevens]

Mac OS 10.3.9 R framework  v. 2.1.1

I am attempting to put a fitted curve into each panel of a lattice 
graph, but am failing to do so. I have tried writing a very 
sophisticated function to do so. The function seems to work when used 
with plot(), but does not do so inside a panel function in xyplot().
Any pointers would be appreciated.

#The example data
fact <- gl(2,7)
x <- rep(1:7,2)
y <- c(1,1,2,3,2,3,4,1,2,1,2,3,3,4)
plot(jitter(y/6) ~ x)

# The following user defined function puts a curve (I believe the 
correct one) into the scatterplot
panel.predglm <- function(x, y) {	
	model.trial <- glm(cbind(y,6-y) ~ poly(x,2), 
family=quasibinomial(link="logit"))
	xfit <- seq(1,7, length=21)
	yfit <- predict(model.trial, newdata=data.frame(x=xfit), 
type="response")
	lines(xfit,yfit)  }

panel.predglm(x, y)


# My attempt to use it in a lattice xyplot, however, fails. It draws a 
curve which in most cases is outside the dimensions of the plot. I 
suspect that the prediction is on the scale of the link functions.

library(lattice)
xyplot(y/6 ~ x|fact, ylim=c(0,.8),
panel=function(x, y,...) {
	panel.xyplot(jitter(x),jitter(y))
	panel.predglm(x,y) }
	)

Any thoughts?
Hank Stevens


Dr. Martin Henry H. Stevens, Assistant Professor
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Botany Department
Miami University
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