[R] "eval" inside a function call in connection with updating the data slot in the call of lmer

[Søren Højsgaard]

Dear list,
Given a linear mixed model (from lme4) I want to 1) first change the input dataset and then 2) change the model formula. I want this to happen in a function call; 
Please see below. Options 1) and 2) below work whereas 3) fails with the message 
> foo()
Error in is.data.frame(data) : object 'beets2' not found

Question: What is it one must to in case 3) to have R look "inside" the function to figure out what "beets2" is?

Best regards 
Søren
________________

library(pbkrtest)
data(beets)
lgs    <- lmer(sugpct~block+sow+harvest+(1|block:harvest), data=beets, REML=F)

foo <- function(){
	## 1)
	beets2 <- transform(beets, yy = sugpct * yield)
	ma1    <- lmer(yy~block+sow+harvest+(1|block:harvest), data=beets2, REML=F)
	ma0    <- update(ma1, yy~.)
	## 2)
	cl <- getCall(lgs)
	cl[["data"]] <- beets2
	mb1 <- eval(cl)
	mb0 <- update(mb1, yy~.)
	mb0
	## 3)
	cl <- getCall(lgs)
	cl[["data"]] <- as.name("beets2")
	mc1 <- eval(cl)
	mc0 <- update(mc1, yy~.)
	mc0
}
foo()