title: Understanding MapReduce Example
body: <p>I am beginner with MapReduce, and currently reading the book Data-Intensive Text Processing with MapReduce by Jimmy Lin and Chris Dyer (<a href="http://lintool.github.io/MapReduceAlgorithms/MapReduce-book-final.pdf" rel="nofollow noreferrer">link to PDF</a>)</p>
  
  <p>Anyways, the first example the book provides is a word counting algorithm, and I am having trouble understanding why the final output of the reducer is what it is. The example is on page number 23 of the text, figure 2.2. To my understanding X should be 6, Y should be 9, and Z should be 19. </p>
  
  <p><img src="https://i.stack.imgur.com/NUthS.jpg" alt=""></p>