Ista:

But I think the problem here is how to update the model formula. I see no
"simple" way to do that (it can be done straightforwardly enough, but I
wouldn't consider it simple).

... But perhaps what you meant is to update the data argument like this:

cntrl <- data.frame(...)  ##response + unchanging base variables

mdl1 <- lm(resp ~ ., data =cntrl)  ## just base covariates

mdlx <- update(mdl1, data = cbind(cntrl, xdat) )  ## where xdat is data
frame with extra covariates.

?formula


Cheers,
Bert

On Wed, Oct 5, 2011 at 12:37 PM, Ista Zahn <izahn@psych.rochester.edu>wrote:

> Hi Justin,
>
> On Wed, Oct 5, 2011 at 3:32 PM, justin jarvis
> <littledude.jarvis@gmail.com> wrote:
> > Hi all,
> > I am running regressions with many covariates, most of which remain the
> same
> > each time (control variables).  Instead of writing 30 demographic
> variables
> > every regression, is there a way I could call them all at once using a
> > variable called, perhaps "demog"?
>
> I would create a base model with just the covariates, and then use
> update() to add other variables.
>
> Best,
> Ista
>
> >
> > I have tried:
> >> demog <- list(age1, age2, age3) but I get an error when I try to call a
> > list in a regression.
> >
> > I also tried:
> >> demog <- cbind(age1, age2, age3) which allows me to run a regression,
> but
> > this is not practical because when I subset the original data set and run
> a
> > regression, this new matrix demog doesn't get subsetted as well, so the
> > variables are of differing length.
> >
> > I'm thinking there is an easy way to do this.  Thanks for any help
> > guys/gals.
> >
> > Justin
> > PhD student,
> > University of California, Irvine
> >
> >        [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>
>
> --
> Ista Zahn
> Graduate student
> University of Rochester
> Department of Clinical and Social Psychology
> http://yourpsyche.org
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
"Men by nature long to get on to the ultimate truths, and will often be
impatient with elementary studies or fight shy of them. If it were possible
to reach the ultimate truths without the elementary studies usually prefixed
to them, these would not be preparatory studies but superfluous diversions."

-- Maimonides (1135-1204)

Bert Gunter
Genentech Nonclinical Biostatistics

	[[alternative HTML version deleted]]

