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
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mmc
meta-method
create-react-native-app
lastindexof
useimperativeref
geoip2
pysmt
qtif
xml-to-json
rtweet
spot-instances
visual-prolog
aws-control-tower
gravity
windows-build-tools
rlwrap
innerhtml
tabletop-simulator
appassembler
react-animated
cross-browser
android-intent-chooser
lightsail
phplint
adornerdecorator
template-aliases
r2rml
harbor
exec
