R devel - Jan 2010 - Wishlist: system.file(... package) throw an error if package not installed/path not found

Currently, system.file() on a non-existing package returns an empty string:

path <- system.file(package="foo");
print(path);
[1] ""

The same goes for non-existing paths in existing package directories:

path <- system.file("foo", package="base");
print(path);
[1] ""

Is there a rationale for this, or is it just for historical reasons?
Is the empty string "" used in R to represent a "missing"
file?  (e.g.
file.exists("") == FALSE).

I would like to suggest that an error is thrown instead, so that it is
caught as soon as possible and not down stream.

/Henrik

On Jan 14, 2010, at 15:01 , Henrik Bengtsson wrote:
> Currently, system.file() on a non-existing package returns an empty  
> string:
>
> path <- system.file(package="foo");
> print(path);
> [1] ""
>
> The same goes for non-existing paths in existing package directories:
>
> path <- system.file("foo", package="base");
> print(path);
> [1] ""
>
> Is there a rationale for this, or is it just for historical reasons?
> Is the empty string "" used in R to represent a
"missing" file?  (e.g.
> file.exists("") == FALSE).
>
> I would like to suggest that an error is thrown instead, so that it is
> caught as soon as possible and not down stream.
>
I cannot answer for the original author, but throwing an error is  
generally a very bad idea since it defeats the vectorization. It is  
much easier to simply use if(nzchar(system.file(...))) if you want to  
throw an error in a scalar context than to lose all results because of  
one vector entry. And, yes, file.exists("") will indeed return FALSE  
(although it is entirely unrelated).

Cheers,
Simon