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.

Solution

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)

Comments

[Roland]

The second option is prefered and usually safer.

[Abel Callejo]

This answer doesn't tell about First of all, what is a S4 class?

[slamballais]

@AbelCallejo That's because the S4 object has nothing to do with What am I doing wrong here?. It's just the error that OP got from misapplying the code, and it could have been a completely different error had OP used a different function than ctree.

[Gregor Thomas]

... or even simpler ctree(sex ~ ahe, data = d)?

[slamballais]

@Gregor-reinstateMonica That could also work, but OP specifically used a string and as.formula. (This setup has the unique advantage that you can make strings a priori and then supply them to a function that takes formulas, whereas your answer is hard-coded.)