[Rd] add "select" to subset docs (PR#6710)

[ivo.welch at yale.edu]

Full_Name: ivo welch
Version: current
OS: linux
Submission from: (NULL) (130.132.33.212)



* In the ?subset page, please add

      subset( dataframe, select= c(-column1,-column2) )

       returns a dara frame that is without columns 1 and 2 .

* Also, in ?lm, it would be nice to add a few more words about how to get a
residuals vector of the same length as the variable vectors, even if there are
NAs.  (I know how to do this in one way, but this may not be the right
recommended way.)

I figure that I can help with suggestions for the docs more than with the
substance, being an R learner myself.  It's a truly amazing language.

regards,

/ivo