Update the book

Author: garrettgman

docs/preface.html

@@ -360,7 +360,7 @@ <h1>Preface</h1>
 - Greg Snow</p>
 </blockquote>
 <p>Greg compares R to SPSS, but he assumes that you use the full powers of R; in other words, that you learn how to program in R. If you only use functions that preexist in R, you are using R like SPSS: it is a bus that can only take you to certain places.</p>
-<p>This flexibility matters to data scientists. The exact details of a method or simulation will change from problem to problem. If you cannot build a method tailored to your situation, you may find yourself tempted to make unrealistic assumptions just so you can you use an ill-suited method that already exists.</p>
+<p>This flexibility matters to data scientists. The exact details of a method or simulation will change from problem to problem. If you cannot build a method tailored to your situation, you may find yourself tempted to make unrealistic assumptions just so you can use an ill-suited method that already exists.</p>
 <p>This book will help you make the leap from bus to car. I have written it for beginning programmers. I do not talk about the theory of computer science—there are no discussions of big <code>O()</code> and little <code>o()</code> in these pages. Nor do I get into advanced details such as the workings of <em>lazy evaluation</em>. These things are interesting if you think of computer science at the theoretical level, but they are a distraction when you first learn to program.</p>
 <p>Instead, I teach you how to program in R with three concrete examples. These examples are short, easy to understand, and cover everything you need to know.</p>
 <p>I have taught this material many times in my job as Master Instructor at RStudio. As a teacher, I have found that students learn abstract concepts much faster when they are illustrated by concrete examples. The examples have a second advantage, as well: they provide immediate practice. Learning to program is like learning to speak another language—you progress faster when you practice. In fact, learning to program <em>is</em> learning to speak another language. You will get the best results if you follow along with the examples in the book and experiment whenever an idea strikes you.</p>