I have received a great deal of feedback from a number of people for various errors, typos, and dumb things. Thank you to all of the people who have offered their feedback. I am happy that so many people have found this a useful resource.
I have also written a book about programming R. If you would like to have an additional resource in another form, please take a look and consider it for additional help: R Object Oriented Programming. It is published by Packt Publishing.