aggregate(as.formula("some formula"), data, function) error when called from in a function

I'm having a problem with aggregate.formula when I call it in a function and the function is converted from a string in the funtion

I think my problem may also only occur when the left hand side of the formula is cbind(...)

Here is example code that generates a dataset and then the error.

The first function "agg2" fails

agg2(FALSE)

do agg 2
Error in m[[2L]][[2L]] : object of type 'symbol' is not subsettable

but, if I run it have it return what it is going to pass to aggregate and pass it myself, it works. I can use this for a workaround (agg3) where one function does this itself.

I'm confused by the behavior. Is there some way to not have to use a separate function to make the call ?


======================
# start R code
# idea: in a function, count the number of instances
# of some factor (y) associated with another
# factor (x). aggregate.formula appears to be
# able to do this... but I have a problem if all of the following:
# (1) It is called in a function
# (2) the formula is created using as.formula(character)
# calling aggregate with the same formula (created with as.formula)
# outside the function works fine.
agg2 <- function(test=FALSE) {
?# create a factor y
?dat <- data.frame(y=sample(LETTERS[1:3],100,replace=TRUE))
?# create a factor x
?dat$x <- sample(letters[1:4],100,replace=TRUE)
?# make a column of 1s and zeros
?# 1 when that row has that level of y
?# 0 otherwise
?lvls <- levels(dat$y)
?dat$ya <- 1*(dat[,1] == lvls[1])
?dat$yb <- 1*(dat[,1] == lvls[2])
?dat$yc <- 1*(dat[,1] == lvls[3])
?# this works fine if you give the exact function
?agg1 <- aggregate(cbind(ya,yb,yc)~x,data=dat,sum)
?# and fine if you accept
?fo <- as.formula("cbind(ya,yb,yc)~x")
?if(test) {
? ? ? ?return(list(fo=fo,data=dat))
?}
?cat("do agg 2\n")
?agg2 <- aggregate(fo,data=dat,sum)
?list(agg1,agg2)
}
agg2(FALSE)
ag <- agg2(TRUE)
ag$fo
aggregate(ag$fo,ag$data,sum)


agg3 <- function() {
?ag <- agg2(TRUE)
?ag$fo
?aggregate(ag$fo,ag$data,sum)
}
agg3()

# end R code
==============
Paul Bailey
University of Maryland