R help - Dec 2002 - How to get objects from a "formula" specification?

Hi:

I'd like to get the objects corresponding to the elements in a formula, 
from a data frame.  For example, suppose I would like to make a 
function call, such as follows:

myfunc(formula="y ~ x1 + x2 + log(x3)" , data=mydata)

This function will get the vector objects y, x1, x2, and log(x3) from 
the data frame "mydata" to form the design matrix and then perform a 
maximum likelihood estimation of the regression parameters.  

My questions is,  how do I get the the vector objects y, x1, x2, and 
log(x3),specified the formula, from the data frame "mydata"?

thanks for any help,
Ravi.

?model.frame
?model.matrix

`S Programming' by Venables & Ripley (2000).

On Fri, 13 Dec 2002, Ravi Varadhan wrote:
> Hi:
>
> I'd like to get the objects corresponding to the elements in a formula,
> from a data frame.  For example, suppose I would like to make a
> function call, such as follows:
>
> myfunc(formula="y ~ x1 + x2 + log(x3)" , data=mydata)
>
> This function will get the vector objects y, x1, x2, and log(x3) from
> the data frame "mydata" to form the design matrix and then
perform a
> maximum likelihood estimation of the regression parameters.
>
> My questions is,  how do I get the the vector objects y, x1, x2, and
> log(x3),specified the formula, from the data frame "mydata"?
BTW, that's not precisely how formulae in R work.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

I'd like to thank Prof. Ripley and Andy Liaw for their solution to my 
question. They suggested using "model.frame" or
"model.matrix"

Best,
Ravi.
----- Original Message -----
From: ripley at stats.ox.ac.uk
Date: Friday, December 13, 2002 12:44 pm
Subject: Re: [R] How to get objects from a "formula" specification?
> ?model.frame
> ?model.matrix
> 
> `S Programming' by Venables & Ripley (2000).
> 
> On Fri, 13 Dec 2002, Ravi Varadhan wrote:
> 
> > Hi:
> >
> > I'd like to get the objects corresponding to the elements in a 
> formula,> from a data frame.  For example, suppose I would like to 
> make a
> > function call, such as follows:
> >
> > myfunc(formula="y ~ x1 + x2 + log(x3)" , data=mydata)
> >
> > This function will get the vector objects y, x1, x2, and log(x3) 
> from> the data frame "mydata" to form the design matrix and
then
> perform a
> > maximum likelihood estimation of the regression parameters.
> >
> > My questions is,  how do I get the the vector objects y, x1, x2, and
> > log(x3),specified the formula, from the data frame "mydata"?
> 
> BTW, that's not precisely how formulae in R work.
> 
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272860 (secr)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
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>