We'll do a really common Spark and MapReduce example of dealing with a book or text file. We'll count all the words in a text file and find out how many times each word occurs within that text. We'll put a little bit of twist on this task and work our way up to doing more and more complex twists later on. The first thing we need to do is go over the difference again between map and flatMap, because using flatMap and Spark is going to be the key to doing this quickly and easily. Let's talk about that and then jump into some code later on and see it in action.
For the next few sections in this book, we'll look at your standard "count the words in a text file" sample that you see in a lot of these sorts of books, but we're going to do a little bit of a twist. We'll work our way up from a really simple implementation of counting the words, and keep adding more and more stuff to make that even better as we go along. So, to start off with...