R package dependencies

Hi Colin,

The pkgDepTools package from Bioconductor will help with question
#1:

http://bioconductor.org/packages/2.5/bioc/html/pkgDepTools.html

I am not positive on this, but I believe this package is also used
to determine the reverse dependencies that would be listed on that
page if there were any for this package. An example with reverse
dependencies is e.g., the IRanges package:

http://bioconductor.org/packages/2.5/bioc/html/IRanges.html

The maintainer (Seth Falcon) would know for sure if the package will
do reverse dependencies as well.

The edge directions of the dependency graph can be reversed and the
resulting graph used to determine the set of packages that make use
of (even indirectly) a given package. For example, one might like to
know which packages make use of the methods package. Here is one way
to do that: <example follows in the vignette>