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
bcc-bpf
low-level-api
git-rm
oledbconnection
vscode-jsconfig
functional-programming
xbox360
vorbis
google-analytics-filters
spdy
system.reflection
jenkins-plugins
uiculture
cl
throwable
io.js
fantomas
actionviewhelper
aws-codecommit
firebase-extensions
objectlistview-python
inappbrowser
cxxtest
lda
google-sheets
dbus-python
autosize
moleculer
astoria
microsoft-exchange