[R] Checking whether specific packages (from bioconductor) are installed when loading a package

[Søren Højsgaard]

Dear all,

My package 'gRbase' uses three packages from Bioconductor and these are not automatically installed when gRbase is installed. My instructions (on the package webpage) to users are therefore to run:

source("http://bioconductor.org/biocLite.R"); biocLite(c("graph","RBGL","Rgraphviz"))

When loading gRbase, it is checked whether these Bioconductor packages are available, but I would like to add a message about how to install the packages if they are not.

Does this go into .onAttach or .onLoad or elsewhere?

Thanks in advance
Søren