In this section, you will learn how tables are represented in R and how you can work with tabular objects. In particular, you will learn two common ways to create table objects (from vectors or by reading a file from the disk). Afterwards, you will learn how to examine, subset, and make calculations with tables.
The data.frame class is the basic class to represent tabular data in R. A data.frame object is essentially a collection of vectors, all with the same length. However, the vectors do not have to be of the same type. They may also include one-dimensional objects that are not strictly vectors, such as Date or factor objects (see the previous chapter). Therefore, data.frame objects are particularly suitable to represent data with different variables in columns and different cases in rows. Thus, variables may be of different types; for example, a table storing climatic data may have one character...