Merge pull request #2 from blairj09/patch-1

Update preface.rmd

preface.rmd

@@ -14,7 +14,7 @@ Not every programmer needs to be a data scientist, so not every programmer will
 
 One of the biggest surprises in this book is that I do not cover traditional applications of R, such as models and graphs; instead, I treat R purely as a programming language. Why this narrow focus? R is designed to be a tool that helps scientists analyze data. It has many excellent functions that make plots and fit models to data. As a result, many statisticians learn to use R as if it were a piece of software—they learn which functions do what they want, and they ignore the rest. 
 
-This is an understandable approach to learning R. Visualizing and modeling data are complicated skills that require a scientist's full attention. It takes expertise, judgement, and focus to extract reliable insights from a data set. I would not recommend that any any data scientist distract herself with computer programming until she feels comfortable with the basic theory and practice of her craft. If you would like to learn the craft of data science, I recommend the book [R for Data Science](http://r4ds.had.co.nz/), my companion volume to this book, co-written with Hadley Wickham.
+This is an understandable approach to learning R. Visualizing and modeling data are complicated skills that require a scientist's full attention. It takes expertise, judgement, and focus to extract reliable insights from a data set. I would not recommend that any data scientist distract herself with computer programming until she feels comfortable with the basic theory and practice of her craft. If you would like to learn the craft of data science, I recommend the book [R for Data Science](http://r4ds.had.co.nz/), my companion volume to this book, co-written with Hadley Wickham.
 
 However, learning to program _should_ be on every data scientist's to-do list. Knowing how to program will make you a more flexible analyst and augment your mastery of data science in every way. My favorite metaphor for describing this was introduced by Greg Snow on the R help mailing list in May 2006. Using functions in R is like riding a bus. _Writing_ functions in R is like driving a car.
 
@@ -67,4 +67,4 @@ Further ideas came from the students and teachers of Introduction to Data Scienc
 
 Thank you also to JJ Allaire and the rest of my colleagues at RStudio who provide the RStudio IDE, a tool that makes it much easier to use, teach, and write about R.
 
-Finally, I would like to thank my wife, Kristin, for her support and understanding while I wrote this book.
+Finally, I would like to thank my wife, Kristin, for her support and understanding while I wrote this book.