Inference from tables by joining, reshaping, and aggregating

In this section, you will learn several more advanced operations involving tables. These include, in particular, reshaping of tables and joining the information from table pairs. The presented methods, together with the ones presented earlier, will compose quite a powerful toolbox, which will suffice for all table-related operations that you will use in this book. Since you will be using functions from contributed packages, you will first learn how to download and install them. The following three sections will then introduce functions to reshape, aggregate, and join tables, respectively.

Using contributed packages

All predefined objects in R (such as the functions and classes we have been using so far) are collected in libraries or packages (in R terminology). In order to use an object defined in a certain package, it first needs to be loaded into memory. This is done using the library function. So far, we did not use the library...