Book Image

R Object-oriented Programming

By : Black
Book Image

R Object-oriented Programming

By: Black

Overview of this book

This book is designed for people with some experience in basic programming practices. It is also assumed that they have some basic experience using R and are familiar using the command line in an R environment. Our primary goal is to raise a beginner to a more advanced level to make him/her more comfortable creating programs and extending R to solve common problems.
Table of Contents (14 chapters)
4
4. Calculating Probabilities and Random Numbers
12
A. Package Management
13
Index

Defining indexing operations

An object that is a Course class can have many assignment objects in its Grades slot. We did not define a special method to get a particular assignment, and no method is defined to save an assignment. We examine how to do this is in this section, and the discussion revolves around redefining the [ operation.

First we redefine the [ operation used to get an assignment. The idea is that we want to get a copy of an assignment by enclosing the name of the assignment as defined in the original file within square braces. To do this, we can redefine the operation. In this case, we want to be able to pass any kind of object within the braces, which will allow us to also use integers to index by location in the list:

setMethod("[",
          signature(x="Course",i="ANY"),
          definition=function(x,i=1)
          {
              #print(paste("Get grade item",i))
              return(x@Grades[[i]])
          }
          )

We would...