data(Atrazine)
cenfit(Atrazine$Atra, Atrazine$AtraCen)
cenfit(Atrazine$Atra, Atrazine$AtraCen, Atrazine$Month)
cenfit(Cen(Atrazine$Atra, Atrazine$AtraCen))
cenfit(Cen(Atrazine$Atra, Atrazine$AtraCen)~Atrazine$Month)
Run the code above in your browser using DataLab