From: Rolf Turner <rolf_at_math.unb.ca>

Date: Fri 03 Jun 2005 - 05:14:34 EST

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jun 03 05:19:40 2005

Date: Fri 03 Jun 2005 - 05:14:34 EST

Brian Ripley wrote:

> <snip> But the real problem is more likely that Rolf has not passed

*> model.matrix a model frame, so it calls model.frame() internally. The
**> help page is a bit confused in that it says
**>
**> data: a data frame created with 'model.frame'.
**>
**> which the default for the argument is not. So a better solution would
**> then be to call model.frame and pass a model frame to model.matrix.
**>
**> delete.response() might also be useful.
**>
**> The suggested warning only applies if `data' is not supplied.
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I don't grok this. I ***did*** supply data (in the form of a data frame, not a model frame). My call was of the form X <- model.matrix(fmla,XXX) where (originally) ``fmla'' was a formula with the structure ``y ~ x + w + z'', and XXX was a data frame with columns ``y'', ``x'', ``w'', and ``z''. (The response variable ``y'' had NAs in it, which caused the problem.) The data frame XXX was ``input data''; it was not created with model.frame, but it was data nonetheless. I replaced the forgoing call with X <- model.matrix(fmla[-2],XXX) (the ``-2'' causing the ``y'' part of the formula to be discarded) and got the results I wanted. There may be a better way of achieving my goal, but I'm happy with my method --- unless someone points out lurking hazzards that have so far not been apparent to me. I merely wanted to point out to others the somewhat unintuitive behaviour of model.matrix. cheers, Rolf Turner rolf@math.unb.ca ______________________________________________R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jun 03 05:19:40 2005

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