[R] How to avoid searching variables in global environment

Duncan Murdoch murdoch.duncan at gmail.com
Fri Sep 13 00:19:33 CEST 2013


On 12/09/2013 5:54 PM, Gang Peng wrote:
> Hi Bill,
>
> Thanks. I think we can define the function in the environment whose parent
> environment is empty environment. But don't know how.

You can say environment(f) <- emptyenv()

but then almost nothing will work.  You wanted a+b.  It won't know what 
+ is.

Duncan Murdoch
>
> Best,
> Mike
>
>
>
>
> 2013/9/12 William Dunlap <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
> >
> >
> > > -----Original Message-----
> > > From: 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
> > > 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>
> > 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.
> >
>
> 	[[alternative HTML version deleted]]
>
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