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.
Thanks,
Michael
2013/9/12 Bert Gunter <gunter.ber...@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.gos...@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.p...@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@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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