[R] About source()

[Uwe Ligges]

On 03.01.2012 07:50, Rolf Turner wrote:
> On 03/01/12 17:02, Li SUN wrote:
>> Hello,
>>
>> I am a beginner to the R language and find it fantastic and
>> well-designed, quite different from other programming languages.
> What a refreshingly sensible attitude!!! :-)
>> This is the first time I post on the r-help mailing list.
>>
>> In invoking the function source(filename), it seems that the filename
>> has to exist in the current working directory, otherwise it has to be
>> specified in full path.

No: relative (to the working directory) specifications are possible as well.

Uwe Ligges



>> So is there any mechanism(such as environment
>> variable) to specify an additional directory of .R files that source()
>> could search in?
>
> I'm no expert on this, and others may correct me, but
>
> (1) I don't believe any such mechanism exists.
>
> (2) It's probably not a good idea, even if such a mechanism
> were to exist. Directories have a tree structure, rather than
> being linearly ordered in the way that data bases on your
> R search path are ordered.
>
> I believe you would run all sorts of risks of confusion and
> of getting the wrong file were you to invoke such a mechanism.
>
> It is ``good practice'' to have separate directories associated
> with different projects and to situate all files, that you might wish
> to source in respect of a given project, in the directory associated
> with that project.
>
> I know that this is an irritating sort of response --- ``No, you can't
> do that, and you shouldn't do it anyway!'' --- but I sincerely believe
> this to be true.
>
> That being said, I also believe that you could program up such a mechanism
> yourself. I.e. build a function "source2()" which would have a "hard
> coded" list
> of directories to search, and would make use of the "try()" function.
>
> Might be a good exercise for you, given that you are starting out in R
> and looking to upgrade your skills! :-)
>
> cheers,
>
> Rolf Turner
>
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