[R] How to avoid searching variables in global environment

[William Dunlap]

Typo: in 
    environment(fun) <- new.env(parent=parent.env())
the parent.env() should have been emptyenv().  But, as
I said, you do not want to do that.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of William Dunlap
> Sent: Thursday, September 12, 2013 3:19 PM
> To: Gang Peng
> Cc: r-help at r-project.org
> Subject: Re: [R] How to avoid searching variables in global environment
> 
> You can do that with
>    environment(fun) <- new.env(parent=parent.env())
> but then your function, function(b)a+b, will not be able
> to find the "+" function.
> 
> Putting this code into a package simplifies things a lot.
> 
> E.g., I added a file containing the two lines
>    phi <- sum(1/(1:1e6)) - log(1e6) # 0.5772...
>    fun <- function(b) a + b + phi
> to a package (and added phi and fun to the NAMESPACE file's export
> command).  Then R CMD check myPackage reported
>    * checking R code for possible problems ... Note
>    fun: no visible binding for global variable 'a'
> It did not complain about the "+" or "phi", since they are
> either in the package or in some package required by my
> package but it did complain about the "a".
> 
> Furthermore, at runtime, fun will always get phi from the package,
> even if I happen to have a phi in  my global environment.
>   > fun(10)
>   Error in fun(10) : object 'a' not found
>   > a <- 1000
>   > fun(10) # uses .GlobalEnv's a
>   [1] 1010.577
>   > phi <- 100
>   > fun(10) # still uses myPackage's phi
>   [1] 1010.577
> 
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
> 
> From: Gang Peng [mailto:michael.gang.peng at gmail.com]
> Sent: Thursday, September 12, 2013 2:54 PM
> To: William Dunlap
> Cc: Sarah Goslee; r-help at r-project.org
> Subject: Re: [R] How to avoid searching variables in global environment
> 
> Hi Bill,
> 
> Thanks. I think we can define the function in the environment whose parent environment
> is empty environment. But don't know how.
> Best,
> Mike
> 
> 
> 2013/9/12 William Dunlap <wdunlap at tibco.com<mailto:wdunlap at tibco.com>>
> If you want to find out if you've forgotten to make 'a' an argument
> you can use codetools::findGlobals(func) to list the names that don't
> refer to something already defined in the 'func':
>   > fun <- function(b) a + b
>   > library(codetools)
>   > findGlobals(fun)
>   [1] "+" "a"
> You need to filter out things defined in some attached package (like the "+"
> from the base package).  I think that when you run 'R CMD check' on a
> package this sort of check is made on the functions in the package.
> findGlobals does not run the function to make its checks, it just looks at
> the function.
> 
> A kludgy way to get an error message instead of having the function silently
> use something from .GlobalEnv is to make the environment of the function
> the parent of .GlobalEnv
>    >  a <- 1000
>    > environment(fun) <- parent.env(globalenv())
>    > fun(7)
>    Error in fun(7) : object 'a' not found
> Since this is a run-time check it will not find problems in branches of the
> code that are not run.  The parent environment of .GlobalEnv changes
> every time you attach or detach a package.  For production code you will
> want to use a package - the namespace mechanism and the check command
> will take care of most of this sort of problem.
> 
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com<http://tibco.com>
> 
> 
> > -----Original Message-----
> > From: r-help-bounces at r-project.org<mailto:r-help-bounces at r-project.org> [mailto:r-
> help-bounces at r-project.org<mailto:r-help-bounces at r-project.org>] On Behalf
> > Of Sarah Goslee
> > Sent: Thursday, September 12, 2013 2:09 PM
> > To: Gang Peng
> > Cc: r-help at r-project.org<mailto:r-help at r-project.org>
> > Subject: Re: [R] How to avoid searching variables in global environment
> >
> > 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<mailto: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<mailto: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.
> 
> 
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