[R] lm() and interactions in model formula for x passed as matrix

William Simpson william.a.simpson at gmail.com
Sun Dec 5 21:19:05 CET 2010

Suppose I have x variables x1, x2, x3 (however in general I don't know
how many x variables there are). I can do
lm(y ~ X)
This fits the no-interaction model with b0, b1, b2, b3.

How can I get lm() to fit the model that includes interactions when I
pass X to lm()? For my example,
I am looking for something along the lines of
lm(y~X ...)
where ... is some extra stuff I need to fill in.

Thanks for any help.

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