[Rd] y ~ X -1 , X a matrix

Ross Boylan ross at biostat.ucsf.edu
Thu Mar 18 00:32:41 CET 2010

While browsing some code I discovered a call to lm that used a formula y
~ X - 1, where X was a matrix.

Looking through the documentation of formula, lm, model.matrix and maybe
some others I couldn't find this useage (R 2.10.1).  Is it anything I
can count on in future versions?  Is there documentation I've

For the curious: model.frame on the above equation returns a data.frame
with 2 columns.  The second "column" is the whole X matrix.
model.matrix on that object returns the expected matrix, with the
transition from the odd model.frame to the regular matrix happening in
an .Internal call.


P.S. I would appreciate cc's, since mail problems are preventing me from
seeing list mail.

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