[R] findGlobals on apply

[Gabor Grothendieck]

I think what he is referring to is that findGlobals lists mean under
variables rather than functions when you do this with his f:

> findGlobals(f, FALSE)
$functions
[1] "{"     "apply"

$variables
[1] "mean"

On Tue, Apr 8, 2008 at 7:14 AM, Duncan Murdoch <murdoch at stats.uwo.ca> wrote:
> Christophe Genolini wrote:
> >>> f <- function(x){apply(x,2,mean)}
> >>> findGlobals(f)
> >>>
> >> mean is a global variable, so findGlobals gets it right.
> >>
> > That sound strange to me: a "variable" is something that vary... mean
> > does not vary. maen will ge an argument that is a line of x and will
> > make some calculous on it, that is the comportement of a function.
> > Of course, mean is an argument of an other function, but I do not think
> > this is a reason good enouth to say that mean is a variable.
> >
>
> findGlobals doesn't try to tell what mean is; it's just reporting on how
> you've used it.  Your usage means that the interpreter will treat it as
> a variable, getting a copy of its value and passing it as an argument to
> apply.  (That's an oversimplification, of course:  it's very unlikely
> that an actual copy will be made, but it will act as if one was made.)
>
> > Furthemore, I use findGlobals to detect some typo. In
> >
> > f <- function(myObject){return(mObject^2)}
> >
> > findGlobals will detect that mObject is a global so I know there is a
> > typo somewhere.
> > Considering mean as a globals do not let us use findGlobals this way.
> >
> >
>
> You can still use it to detect that kind of typo, but you need a second
> step where you check whether the globals exist in the environment of the
> function or not.  That test won't be perfect either:  it will miss cases
> where you meant to type a local variable, but by mistake typed the name
> of some global.  Most uses of mean as a variable would fall into that
> category; unfortunately (?) apply means some of them are legitimate.
>
> I think the best you'll ever be able to do is to get some suggestions of
> errors, with both false positives and false negatives.  If there were
> cases where some usage was definitely an error, the parser would
> probably catch it.
>
> Duncan Murdoch
>
>
>
> > Christophe
> >
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> >
>
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> and provide commented, minimal, self-contained, reproducible code.
>