Kinds of Objects
Part II covers the different kinds of objects that are used in R in terms of their two important qualities: mode and class.
Chapter 4 lists the modes and describes the common ones. In addition to listing all of the modes current in R, the chapter describes the properties of the atomic modes—NULL, raw, logical, numeric, complex, and character—and of the nonatomic modes list, function, call, name, and expression.
Chapter 5 introduces the classes and gives the properties of several of them. The chapter includes a special section on vectors, which are not a class but, a very common kind of object. The classes associated with vectors are raw, logical, integer, double, complex, character, some lists, and expressions. For most atomic objects, the mode and the class are the same. After describing vectors, we give properties of the classes for matrices, arrays, time series, factors, data frames, dates, and times and dates.
Part II concludes with information about assigning names to the dimensions of vectors, matrices, arrays, and lists.