[R] how to check if a library is loaded, from a function

[David Winsemius]

On Jan 31, 2011, at 11:04 PM, Nick Matzke wrote:

> Hi,
>
> I've written a function which I load with a source command.  The  
> function requires a certain library, phangorn, to work.
>
> I would like the function to check if phangorn is loaded as a  
> library before running.  For some reason, just putting  
> require(phangorn) into the sourced function doesn't do anything.

If a package is already loaded then require() will not load it again.  
I think it is also going to be quiet if it's called in a sourced  
routine, so I would ask whether you have properly tested your claim  
that it "doesn't do anything"? If you start with a clean session and  
source your routine, does the routine fail because the package does  
not load?

>
> This must be simple, but I can't figure it out!  Any help  
> appreciated...
>
> -- 
> ====================================================
> Nicholas J. Matzke
> Ph.D. Candidate, Graduate Student Researcher

30 line sig elided.
-- 

David Winsemius, MD
West Hartford, CT