You used variable names 'Date' and 'Cult' in lm2, but *different* names 'Cultc52' and 'Dated16' for prediction.
Regards, Yihui -- Yihui Xie <[EMAIL PROTECTED]> Phone: +86-(0)10-82509086 Fax: +86-(0)10-82509086 Mobile: +86-15810805877 Homepage: http://www.yihui.name School of Statistics, Room 1037, Mingde Main Building, Renmin University of China, Beijing, 100872, China On Sun, Oct 5, 2008 at 11:33 AM, andyer weng <[EMAIL PROTECTED]> wrote: > Hi all, > > I am kind of stuck of using Predict function in R to make prediction > for a model with continuous variable and categorial variables. i have > no problem making the model, the model is e.g. > > cabbage.lm2<- lm(VitC ~ HeadWt + Date + Cult) > > HeadWt is a continuous variable, Date and Culte are factors. Date have > three levels inside (d16,d20,d21), Cult has two levels(c39,c52). I > need to calculate a confidence interval for the mean VitC for each > combination of Date and Cult, fixing the value of HeadWt at the mean > for the corresponding cell. I have already proved that Cult and Date > are not interacted. the mean of HeadWt is also found. e.g.2.59 > > when i type > >> new.df<-data.frame(HeadWt=2.59,Cultc52=1,Dated16=1) >> predict(cabbage.lm2,new.df, interval="confidence") > > it has error comes up like this: > Error in model.frame.default(Terms, newdata, na.action = na.action, > xlev = object$xlevels) : > variable lengths differ (found for 'Cult') > In addition: Warning message: > 'newdata' had 1 rows but variable(s) found have 60 rows > > > Is there anything I have done wrong?? Please help with the coding. > > Thank you so much!!! > > All the best. > > Andyer. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
