[R] How to use lm.predict to obtain fitted values?

Larry Howe larry.howe at comjet.com
Sat May 20 20:48:03 CEST 2006

On Friday 19 May 2006 17:35, Peter Ehlers wrote:
> Larry Howe wrote:
> > I have had a similar issue recently, and looking at the archives of this
> > list, I see other cases of it as well. It took me a while to figure out
> > that the variable name in the data frame must be identical to the
> > variable name in the model. I don't see this mentioned in the
> > documentation of predict.lm, and R issues no warning in this case.
> >
> > How would I go about officially requesting that this is mentioned, either
> > in the documentation, or as a warning?
> >
> > Sincerely,
> > Larry Howe
> Here's what I would do before officially requesting anything: read
> 'An Introduction to R', especially section 11.3:
>   predict(object, newdata=data.frame)
>   The data frame supplied must have variables specified with the same
>   labels as the original.
> Seems pretty explicit.
> As well, the predict.lm help page has, under Arguments:
>   newdata   An optional data frame in which to look for variables with
>             which to predict.
> That, too, seems unambiguous; i.e. you can't predict with values of z
> when z is not in your formula.
> Peter Ehlers

My fault, I should have read ALL the manuals before posing my question. I only 
read the 2445 page Reference Manual. I also read Intro to R, but that was 
some time ago.

"An optional data frame in which to look for variables with which to predict." 
means almost nothing to me. Specifically it doesn't translate to me, as an 
engineer and software developer, but not a statistician, that the names have 
to match, and furthermore if they don't match, R fails silently.

Larry Howe

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