[R] pulling items out of a lm() call

From: Andrew Gelman <gelman_at_stat.columbia.edu>
Date: Mon 01 May 2006 - 20:46:59 EST


I want to write a function to standardize regression predictors, which will require me to do some character-string manipulation to parse the variables in a call to lm() or glm().

For example, consider the call
lm (y ~ female + I(age^2) + female:black + (age + education)*female).

I want to be able to parse this to pick out the input variables ("female", "age", "black", "education"). Then I can transform these as appropriate (to get "z.female", "z.age", etc), feed them back into the lm() function, and go from there.

Does anyone know an easy way to pull out the variables? I basically have to parse out the symbols "+", ":", "*", and " ", but there's also the problem of handling parentheses and the I() operator.

Thanks!
Andrew

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Andrew Gelman
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Professor, Department of Political Science
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Received on Mon May 01 20:53:25 2006

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