Some of the R packages required to reproduce the code in this book have external dependencies, which can either be installation or execution dependencies. We will go through the installation of each external dependency in the following sections. Installing external dependencies is not difficult, but it may be an unfamiliar process that requires us to do some work outside of R. Once we install these external dependencies successfully, installing R packages should be easy.
Before we proceed, I just want to say that you won't always know in advance what external dependencies you need before attempting to install an R package. Normally, you will simply try to install the package and see what happens. If no problems arise, then you are all set. If problems do arise, the output from the console will hint you into what you need...
