S-PLUS classifies objects into many different types, such as vectors
and data frames. Some S-PLUS functions treat these different types
differently. For example, the function plot will do a scatterplot if it
receives a numeric vector, a boxplot if it receives a factor, or a series
of plots if it receives regression output (complicated function output,
such as the output from regression, is generally in the form of a list).
This flexibility is called ``object oriented programming''.
All objects have values and attributes. An object's value is what you see when you type the name of the object, and attributes are things like length (for vectors), dimensions (for a matrix), or row and column labels (for a data frame). The most common objects and their attributes are described below.