[R] findGlobals on apply

[Duncan Murdoch]

On 4/8/2008 7:42 AM, Gabor Grothendieck wrote:
> 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"

Yes, I understood that, and I think it's reasonable behaviour. 
findGlobals analyzes the syntax, not the semantics.

Duncan Murdoch

> 
> 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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>> > and provide commented, minimal, self-contained, reproducible code.
>> >
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
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>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.