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.

Generally, when there's a `data` argument, you shouldn't *also* use `$`. — Gregor Thomas, Jan 23 '20 at 22:01

score 8 · Accepted Answer · answered Apr 20 '16 at 08:12

8

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)

answered Apr 20 '16 at 08:12

slamballais

3

The second option is prefered and usually safer. – Roland Apr 20 '16 at 08:22
1

This answer doesn't tell about `First of all, what is a S4 class?` – Abel Callejo Jan 21 '20 at 02:15
1

@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`. – slamballais Jan 23 '20 at 12:40
... or even simpler `ctree(sex ~ ahe, data = d)`? – Gregor Thomas Jan 23 '20 at 22:01
@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.) – slamballais Jan 26 '20 at 10:29

1 Answers1