Classes of Objects
In R, objects belong to classes as well as modes and types. Classes tell something about how an object is structured. S3 and S4 differ with regard to classes. In S3, there are specific classes into which an R objects falls. In S4, the user defines a class for an S4 object. Classes in S3 are called informal classes, whereas classes in S4 are called formal classes. This chapter covers only S3 classes.
Some Basics on Classes
S3 classes are attributes of S3 objects and are not usually assigned by the user. Given an object, the class of the object can be found by using the function class(). If an object has not been given ...