[R] Fitting model with varying number of predictors

[Juni Joshi]

   I  need  to fit a number of models with different number of predictors
   in  each  model.  Say for example, I have three predictors: x1, x2, x3
   and I want to fit three models:

   lm(y~x1+x2)
   lm(y~x2+x3)
   lm(y~x1+x2+x3)

   Instead  of  typing  all  models,  what I want is to create a variable
   which  can  take  the right hand side of the models. I tried this with
   paste function.

   xxx <- paste("x1","x2",sep=+) for the first
   xxx <- paste("x2","x3", sep = +) for the second
   xxx  <-  paste("x1","x2","x2",  sep  = +) for the third and then fit a
   single model

   lm(y~xxx)

   It did not work. Please suggest how to do it.

   Thanks.

   Jun