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

[Gabor Grothendieck]

Try this:

# test data
fo <- y ~ female + I(age^2) + female:black + (age + education) * female

# create a list of form list(y = as.name("z.y"), ...) for use with substitute
L <- sapply(all.vars(fo), function(nm) as.name(paste("z", nm, sep = ".")))
do.call(substitute, list(fo, L))

On 5/1/06, Andrew Gelman <gelman at stat.columbia.edu> wrote:
> 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
>
> --
> Andrew Gelman
> Professor, Department of Statistics
> Professor, Department of Political Science
> gelman at stat.columbia.edu
> www.stat.columbia.edu/~gelman
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