[R] meaning of glm(value ~ .,

[Gavin Simpson]

On Fri, 2009-06-19 at 09:24 -0400, David Winsemius wrote:
> On Jun 19, 2009, at 9:00 AM, onyourmark wrote:
<snip />
> > means and also, I see
> >
> > data=crs$dataset[,c(1:59,922)]
> >
> > I have read that the data argument is optional here
> > "an optional data frame, list or environment (or object coercible by
> > as.data.frame to a data frame) containing the variables in the  
> > model. If not
> > found in data, the variables are taken from environment(formula),  
> > typically
> > the environment from which glm is called"
> >
> > when they say "data", is that meant to include the dependent  
> > variable as
> > well.
> 
> Yes.

It has to be defined in 'data' or the environment of 'formula', so it
depends on what the OP meant by "meant to include". You can include it
in 'data' but don't have to.

> 
> > In other words,
> > in the above statement 'value' is the dependent variable and it is  
> > also
> > column 922 in the data set.
> > Is this correct?
> 
> Yes.

No - you can't say that it is variable 922, or even any of 1:59 or 922
for the reasons mentioned above.

set.seed(123)
dat <- data.frame(A = rnorm(100), B = rnorm(100), C = rnorm(100))
Y <- rpois(100, 2)
mod <- glm(Y ~ ., data = dat[,c(1,3)], family = poisson)
mod

If all you have is this:

mod <- glm(Y ~ ., data = dat[,c(1,3)], family = poisson)

You can't say anything more about Y than that it is either in 'dat' or
in the environment of 'formula ', which in this case is the global
workspace.

G

> 
> > correct
> > Thank you.
> >
> > -- 
> 
> 
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
> 
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