> HC <- groupedData(bid_price ~ factor(Bedroom.s.) | zip_cbsa_name,
+                                 data = HC)
> head(HC)
Grouped Data: bid_price ~ factor(Bedroom.s.) | zip_cbsa_name
    Bedroom.s.                           zip_cbsa_name     bid_price
116          3     Chicago-Naperville-Joliet, IL-IN-WI      4.828314
139          3 Miami-Fort Lauderdale-Pompano Beach, FL      4.382027
144          5         Dallas-Fort Worth-Arlington, TX      5.164786
234          2    Los Angeles-Long Beach-Santa Ana, CA      4.369448
275          4          Houston-Sugar Land-Baytown, TX      5.220356
301          4     Chicago-Naperville-Joliet, IL-IN-WI      4.867534

> HC_fm1 <- lme(log_bid_price ~ as.numeric(Bedroom.s.), data = HC)
Error in getGroups.data.frame(dataMix, groups) :
  invalid formula for groups