[R] How to build a package which loads Rgraphviz (if installed)...

[William Revelle]

Soren,
When  I had an almost identical  problem last 
year.  I also wanted to use Rraphviz but only if 
people had it.

Kurt Hornik suggested that I replace a direct 
call to the function, foo, that uses Rgraphviz 
with

if(require("Rgraphviz"))  foo()

Bill

At 10:23 PM +0200 7/12/08, Søren Højsgaard wrote:
>Dear List,
>I use Rgraphviz for display of graphs in some 
>packages. Since Rgraphviz is no longer on CRAN 
>it needs to be installed from Bioconductor and 
>that is fine, but I have trouble figureing out 
>the following: I create a plot method which - if 
>Rgraphviz is installed - uses Rgraphviz for 
>displaying and otherwise does nothing. This is 
>implemented as:
>
>
>   if (!("package:Rgraphviz" %in% search())){
>     if("Rgraphviz" %in% installed.packages()){
>       require(Rgraphviz)
>     } else {
>       cat("The Rgraphviz package (from 
>Bioconductor) must be installed to display the 
>models\n")
>       return()
>     }
>   }
>  ... else go on and do the plotting...
>
>When I run rcmd check packagename (on Windows XP, using R.2.7.1) I get
>
>* checking for unstated dependencies in R code ... WARNING
>'library' or 'require' calls not declared from:
>   Rgraphviz
>See the information on DESCRIPTION files in the chapter 'Creating R
>packages' of the 'Writing R Extensions' manual.
>
>I can not state Rgraphviz in the Depends-field 
>of the DESCRIPTION file because then the package 
>does not pass the windows checks for going on 
>CRAN. I can not see any solution from "writing R 
>extensions", but I apologize if I have 
>overlooked it. Does anyone have a suggestion on 
>what to do?
>
>Cheers
>Søren
>
>
>
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-- 
William Revelle		http://personality-project.org/revelle.html
Professor			http://personality-project.org/personality.html
Department of Psychology             http://www.wcas.northwestern.edu/psych/
Northwestern University	http://www.northwestern.edu/
Attend  ISSID/ARP:2009               http://issid.org/issid.2009/