[R] extract indep vars from formula

[Bert Gunter]

...perhaps ?all.vars

as in

> form <- y~x+z
> all.vars(form)
[1] "y" "x" "z"

> all.vars(form)[-1]
[1] "x" "z"

-- Bert




On Wed, Nov 7, 2012 at 2:03 PM, Alexander Shenkin <ashenkin at ufl.edu> wrote:
> Hello,
>
> I'm trying to extract the independent variables from a formula.  The
> closest I've been able to come, aside from rolling my own, is the following:
>
>> a = y ~ b * x
>> attr(terms(formula(a)),"variables")
>
> The reason I'm doing this is that I'm building a grid of points that I
> use to construct a 3-d model prediction surface in rgl.  If there are
> more than two independent variables, I need to set the other ones to 0
> in the dataframe for the predict() routine.  In order to do that, I need
> to know what those variables are.
>
> I suspect there's a better way to go about doing what I'm doing (perhaps
> using the model.* family of functions).  But, in the meantime, just
> extracting the independent variables will move me forward.
>
> Thanks,
> Allie
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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