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

[Prof Brian Ripley]

On Mon, 31 Jan 2011, 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.

Do you mean an R package or an OS library (aka DLL)?  I'll assume the 
former, but please do use accurate terminology.

> 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.

Did you check the return value?  It does do something: compute a 
return value.  You can also check

"package:phangorn" %in% search()

> This must be simple, but I can't figure it out!  Any help appreciated...
>
> Cheers!
> Nick
>
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> Nicholas J. Matzke
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
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