Error: $ operator not defined for this S4 class

Question

I'm trying to make a formula and I got the error:

$ operator not defined for this S4 class with R.

First of all, what is a S4 class? What am I doing wrong?

Following the code:

as.formula("ctree(d$sex ~ d$ahe , data = d)")

If you want to reproduce it, the dataset (CSV file) d is available here.

Answer 1

You are giving as.formula the wrong input here. Only d$sex ~ d$ahe should be a formula, so:

ctree(as.formula("d$sex ~ d$ahe"))

Or:

ctree(as.formula("sex ~ ahe"), data = d)