Summary
An extended example making use of S4 classes was examined in this chapter, and a set of classes are defined to read and track the grades for a class. The Course class keeps track of a number of assignments, and it reads the contents of a CSV file and automatically determines which columns are grades and whether or not they are numerical grades or letter grades.
The grades for a particular assignment are kept in one of two classes. The NumericGrade class keeps track of numerical grades, and the LetterGrade class keeps track of letter grades. Both classes are derived from the Assignment base class.
A number of examples were given, and highlights from the code were given. The full set of code can be found on the website associated with this book, and we recommend that you closely examine the code. The three files that include the definitions for this class are the grades.R, ops.R, and overriding.R files.
In the next chapter, another set of classes are developed. The classes in that chapter...
