Dear R helpers:

Sorry to bother for a basic question about model.matrix.
Basically, I want to apply the dummy coding rule in a dataframe with
complete factor levels to another dataframe with incomplete factor levels.
I used model.matrix, but could not get what I want.
The following is an example.

#Suppose I have two dataframe A and B
dfA=data.frame(f1=factor(c('a','b','c')), f2=factor(c('aa','bb','cc')))
dfB =data.frame(f1=factor(c('a','b','b')), f2=factor(c('aa','bb','bb')))
#dfB's factor variables have less number of levels

#use model.matrix on dfA
(matA<-model.matrix(~f1+f2,data=dfA))
#use model.matrix on dfB
(matB<-model.matrix(~f1+f2,data=dfB))
#I actaully like to dummy code dfB using the dummy coding rule defined in
model.matrix(~f1+f2,data=dfA))
#matB_wanted  is below
(matB_wanted<-rbind(c(1,0,0,0,0),c(1,1,0,1,0),c(1,1,0,1,0)) )
colnames(matB_wanted)<-colnames(matA)
matB_wanted
Can someone kindly show me how to get matB_wanted?
Many thanks in advance!

-Sean

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