Thank you Ivan and Ben for your recent further comments.
I think that the current code for the unregistered model.matrix.lme() in
the development version of the car package is pretty robust and
certainly an improvement over what was there before (which returned
incorrect results for non-default contrasts!).
I expect that if someone in R-core picks up the task of writing a
model.matrix.lme() for the nlme package, they would do a better job than
I did, and I'd then be able to retire the version in the car package.
Again, thanks,
John
On 2024-09-23 4:25 p.m., Ben Bolker wrote:
Caution: External email.
I can't tell whether evaluating object$call$data in
environment(object$formula) is a better or worse idea than parent.frame().
I have struggled with this a lot over the years. There is a bunch of
wonky code in lme4, e.g. here
<https://github.com/lme4/lme4/blob/master/R/lmer.R#L814-L838>, that
tries to look for data in different possible locations, but I don't
think anything works perfectly/robustly.
https://stackoverflow.com/questions/14945274/determine-whether-evaluation-of-an-argument-will-fail-due-to-non-existence
On Mon, Sep 23, 2024 at 3:54 PM Ivan Krylov via R-devel
<r-devel@r-project.org> wrote:
В Sun, 22 Sep 2024 10:23:50 -0400
John Fox <j...@mcmaster.ca> пишет:
Evaluating object$call$data in the environment of the suggested
nlme:::model.matrix.lme function may also not work right. Without an
explicit copy of the data, the best environment to evaluate it in
would be parent.frame().
I'm afraid that I don't understand the suggestion. Isn't
parent.frame() the default for the envir argument of eval()? Do you
mean the parent frame of the call to model.matrix.lme()?
Yes, I do mean the parent frame of the model.matrix.lme() function
call. While eval()'s default for the 'envir' argument is
parent.frame(), this default value is evaluated in the context of the
eval() call. Letting model.matrix.lme() call eval() results in the
'envir' being the eval()'s parent, the model.matrix.lme() call frame.
In most cases, model.matrix.lme() works as intended: either lme() has
been given the 'data' argument, so object$data is not NULL and the
branch to eval() is not taken, or 'data' has not been given, so both
object$data and object$call$data are NULL, and NULL doesn't cause any
harm when evaluated in any environment. In the latter case
model.matrix.default() can access the variables in the environment of
the formula.
With keep.data = FALSE, the function may evaluate object$call$data in
the wrong environment:
maybe_model_matrix <- function(X)
model.matrix(lme(distance ~ Sex, random = ~ 1 | Subject, X,
contrasts=list(Sex=contr.sum), keep.data=FALSE))
maybe_model_matrix(Orthodont)
# Error in eval(object$call$data) : object 'X' not found
...but then model.matrix.default doesn't work on such objects either,
and if the user wanted the data to be accessible, they could have set
keep.data = TRUE. I can't tell whether evaluating object$call$data in
environment(object$formula) is a better or worse idea than
parent.frame().
--
Best regards,
Ivan
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