[R] Error in plot.lm

[peter dalgaard]

On Mar 11, 2011, at 20:31 , David Winsemius wrote:

> 
> Are you sure you need I() on the LHS? The I function is designed to avoid the confusion related to the  dual use of the arithmetic operator symbols affecting the construction of the model matrix, but I don't think that applies to the LHS of the formula.
> 
> (See Dalgaard's comments http://finzi.psych.upenn.edu/Rhelp10/2009-March/192018.html if desiring higher authority.)

Dalgaard is somewhat amused at 

(a) being elevated to god-like status
(b) his actual post starting "I don't think you need I() on the LHS, ..."

Anyways, Jeff knows very well that I() is unneeded, but he had issues with other LHS expressions. The I() problem goes away if you put it inside unclass(), which may be a workaround in other cases. Or, perhaps, plot.lm() really ought to do that internally.

-pd 

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com