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
punctuation
certificate-transparency
liferay-7
google-analytics-4
markdoc
hssfworkbook
openflow
discrete
webservices-client
subpartition
rerender
silk-central
cddvd
oim
tf-agent
data.table
twitter-bootstrap-3
rethinkdbdash
firmware
sql-server-ce-4
reactivex
schemdraw
idiorm
symfony-3.3
last-insert-id
security-roles
protocol-handler
frequency-analysis
document-class
xlsxwriter
