[R] user defined panel function

From: Martin Henry H. Stevens <HStevens_at_MUOhio.edu>
Date: Tue 30 Aug 2005 - 05:25:53 EST

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), 
	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.

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

	panel.predglm(x,y) }

Any thoughts?
Hank Stevens

Dr. Martin Henry H. Stevens, Assistant Professor 338 Pearson Hall
Botany Department
Miami University
Oxford, OH 45056

Office: (513) 529-4206
Lab: (513) 529-4262
FAX: (513) 529-4243


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