[R] Error in plot.lm
pdalgd at gmail.com
Fri Mar 11 22:36:09 CET 2011
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.
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