[R] How to avoid searching variables in global environment

[Duncan Murdoch]

On 12/09/2013 5:36 PM, Gang Peng wrote:
> Hi Bert,
>
> Thanks for the explanation.
>
> In R, it first search the local environment and then the parent environment
> until the root environment (empty environment). I have a concern, when I
> write a function, I may write a variable name wrong by typo. But by
> coincidence,
> this variable name is defined in the parent's or the grandparent's
> environment, it is very hard to find this bug (It took me almost a day to
> find out it).  Just don't know why R do it like this.

I think the reasons are mostly historical.

A fix is to use codetools to identify the variables in your function.  
This is almost automatic if you put your code in a package and use  "R 
CMD check" on it.

Duncan Murdoch
>
> Thanks,
> Michael
>
>
>
> 2013/9/12 Bert Gunter <gunter.berton at gene.com>
>
> > Michael and Sarah:
> >
> > 1. Actually the original claim -- that R will search the global
> > environment if it does not find a free variable in the function environment
> > -- is not strictly true. It will search the function's enclosure and then
> > on up the tree of enclosures. In this case, the enclosure was the global
> > environment, but that is not always the case.
> >
> > 2. Sarah has answered one interpretation of your question. Another might
> > be -- how can you do things to throw an error when free variables are
> > encountered in a function. A qualified answer -- qualified, because there
> > are probably some clever ways to set this up that I can't and won't try to
> > think of -- is that you can't: you are defeating R's functional programming
> > paradigm by requesting such behavior. Or to put it another way: don't
> > do/expect this. Follow Sarah's recommendation instead.
> >
> > Cheers,
> > Bert
> >
> >
> > On Thu, Sep 12, 2013 at 2:08 PM, Sarah Goslee <sarah.goslee at gmail.com>wrote:
> >
> >> Hi,
> >>
> >> You need to specify that a is an argument to the function:
> >>
> >> On Thu, Sep 12, 2013 at 3:56 PM, Gang Peng <michael.gang.peng at gmail.com>
> >> wrote:
> >> > For example:
> >> >
> >> > a <- 1
> >> >
> >> > f <- function(b){
> >> >     return(a+b)
> >> > }
> >> >
> >>
> >> f <- function(b, a) {
> >>     return(a+b)
> >> }
> >>
> >> > when we call function f(2), r will search the local environment first,
> >> if
> >> > it cannot find a, it will search global environment, and return 3. How
> >> to
> >> > avoid r searching the global environment and return an error when we
> >> call
> >> > this function?
> >>
> >> The function will now give an error if a is not specified.
> >>
> >> Sarah
> >>
> >> --
> >> Sarah Goslee
> >> http://www.functionaldiversity.org
> >>
> >> ______________________________________________
> >> 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.
> >>
> >
> >
> >
> > --
> >
> > Bert Gunter
> > Genentech Nonclinical Biostatistics
> >
> > Internal Contact Info:
> > Phone: 467-7374
> > Website:
> >
> > http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm
> >
> >
>
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>
> ______________________________________________
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