R help - Mar 2005 - How to force specific variables in all the models using regsubsets

Dear friends,

        I am trying to use R to do Best Subset Regression, I can not force 
seldom variables in all the subsets models. R is always giving wrong 
variables when I include force.in option. 

For example, I like to include X2 & X4 in all the models, but I always get 
X2 & X3. Could anyone please help me on this issue? Thanks in advance.

x<-rnorm(120)
attr(x,'dim')<-c(20,6)
x<-data.frame(x)
regsubsets(X1~X2+X3+X4+X5,data=x,nbest=2,force.in=c(1,3))

Subset selection object
Call: regsubsets.formula(X1 ~ X2 + X3 + X4 + X5, data = x, nbest = 2, 
    force.in = c(1, 3))
4 Variables  (and intercept)
   Forced in Forced out
X2      TRUE      FALSE
X4     FALSE      FALSE
X3      TRUE      FALSE
X5     FALSE      FALSE
2 subsets of each size up to 4
Selection Algorithm: exhaustive


 

Best Regards,
WeiQiang Li

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