# Contrast drop off from factor x in using predict in decision tree in R

#### milk

##### New Member
Hi,
I have tried research about this error warning message for several days without any info, e.g. ": contrasts dropped from factor staffx.f" etc..
as I tried to use newly decision tree model with the predict function on test data within the rpaprt package.

Here are the scripts that I used to create decision tree model :

db$staff.f<- as.factor(db$staff)
...create same for other categorical variables.

contrasts(db$staff.f) = contr.treatment(8) .... create same for other categorical variables. tree<-rpart(L2 ~ .,method = "class", data = Train ) cpok<-db$cptable[which.min(db\$cptable[,"xerror"]),"CP"]

tree.pruned<-prune(db,cp=bestcp)

pred1 <- predict(tree,Testdata,type="class")

Is there certain parts of the scripts that needs to amend? as it is strange to me that the contrast is drop off even though it is used to create dummy variables and also factor has been created to recognize the certain variables. Much grateful for all advice.

Thank you!

#### hlsmith

##### Omega Contributor
I am not overly familiar with rpart, only used it a couple of times. Question, does all of code work up until predict?

What does contrast do, set a reference level?

#### milk

##### New Member
It is suppose to create dummy variables.

#### rogojel

##### TS Contributor
hi,
my guess would be that this has to do with the pruning. Maybe the contrasts are not defined in the pruned tree anymore?

regards