In R, packages play an indispensable role in data analysis and visualization. In fact, R itself is only a tiny core and is built on several basic packages. A package is a container of predefined functions, which are often designed to be general enough to solve a certain range of problems. Using a well-designed package, we don't have to reinvent the wheel again and again, which allows us to focus more on the problem we are trying to solve.
R is powerful not only because of its rich source of packages, but also because of the well-maintained package archive system called The Comprehensive R Archive Network, or CRAN (http://cran.r-project.org/). The source code of R and thousands of packages is archived in this system. At the time of writing, there are 7,750 active packages on CRAN maintained by more than 4,500 package maintainers around the world. Every week, more than 100 packages will be updated and more than 2 million package downloads happen. You can check...
