[Rd] model.frame question

Therneau, Terry M., Ph.D. therneau at mayo.edu
Tue Jun 17 15:24:43 CEST 2014

   So let me ask an r-core opinion.  Should I change the default to model=TRUE?  Survival 
is heavily used and there is something to be said for consistency within the central 
packages.  Sometimes old habits die hard, and there is a "save memory" part of me that 
hates to save a large object that likely won't be used.  Not nearly as relevant today as 
when I started my career.

   I agree that the biggest issue with model=FALSE is when someone asks for predictions 
from a saved fit, perhaps saved weeks ago, and the data has changed under our feet.  I 
have a check in predict.coxph that the number of rows in the data hasn't changed, but 
there really is no defense.

    Aside: This would mean in theory that I could also change the default to y= FALSE.  I 
discovered a few years ago that that won't fly, when I set the default for y to "not 
model"; why keep redundant copies?  Several other packages that depend on survival failed. 
  They assume fit$y is there, without checking.  The iron chains of backwards compatability...

>> >1. The key line, in both model.frame.coxph and model.frame.lm is
>> >      eval(fcall, env, parent.frame())
>> >
>> >and it appear (at least to me) that the parent.frame() part of this is
>> >effectively ignored when fcall is itself a reference to model.frame.
>> >I'd like to understand this better.

> Way back (ca R 1.2.0) an advocate of lexical scoping changed
> model.frame.lm to refer to an environment not a data frame for 'env'.
> That pretty fundamental change means that your sort of example is not a
> recommended way to do this: you are mixing scoping models.

This hasn't left me any wiser.  Can you expand?  As stated in another note the real issue was
	fit <- coxph(formula, data=nd)
         predict(fit, type="expected")

within a user's function.  They, not unreasonably, expected it to work without further 
trickery.  It fails because the model.frame call within predict.coxph cannot find "nd".

>> >2. The modeling functions coxph and survreg in the survival default to
>> >model=FALSE, originally in mimicry of lm and glm; I don't know when R
>   > changed the default to model=TRUE for lm and glm.  One possible response
> I am not sure R ever did: model = TRUE was the default 16 years ago at
> the beginning of the CVS/SVN archive.

> -- 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 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595

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