Text Mining with R

Preface

If you work in analytics or data science, like we do, you are familiar with the fact that data is being generated all the time at ever faster rates. (You may even be a little weary of people pontificating about this fact.) Analysts are often trained to handle tabular or rectangular data that is mostly numeric, but much of the data proliferating today is unstructured and text-heavy. Many of us who work in analytical fields are not trained in even simple interpretation of natural language.

We developed the tidytext (Silge and Robinson 2016) R package because we were familiar with many methods for data wrangling and visualization, but couldn’t easily apply these same methods to text. We found that using tidy data principles can make many text mining tasks easier, more effective, and consistent with tools already in wide use. Treating text as data frames of individual words allows us to manipulate, summarize, and visualize the characteristics of text easily, and integrate natural language processing into effective workflows we were already using.

This book serves as an introduction to text mining using the tidytext package and other tidy tools in R. The functions provided by the tidytext package are relatively simple; what is important are the possible applications. Thus, this book provides compelling examples of real text mining problems.

Outline

We start by introducing the tidy text format, and some of the ways dplyr, tidyr, and tidytext allow informative analyses of this structure:

• Chapter 1 outlines the tidy text format and the unnest_tokens() function. It also introduces the gutenbergr and janeaustenr packages, which provide useful literary text datasets that we’ll use throughout this book.

• Chapter 2 shows how to perform sentiment analysis on a tidy text dataset using the sentiments dataset from tidytext and inner_join() from dplyr.

• Chapter 3 describes the tf-idf statistic (term frequency times inverse document frequency), a quantity used for identifying terms that are especially important to a particular document.

• Chapter 4 introduces n-grams and how to analyze word networks in text using the widyr and ggraph packages.

Text won’t be tidy at all stages of an analysis, and it is important to be able to convert back and forth between tidy and nontidy formats:

• Chapter 5 introduces methods for tidying document-term matrices and Corpus objects from the tm and quanteda packages, as well as for casting tidy text datasets into those formats.

• Chapter 6 explores the concept of topic modeling, and uses the tidy() method to interpret and visualize the output of the topicmodels package.

We conclude with several case studies that bring together multiple tidy text mining approaches we’ve learned:

• Chapter 7 demonstrates an application of a tidy text analysis by analyzing the authors’ own Twitter archives. How do Dave’s and Julia’s tweeting habits compare?

• Chapter 8 explores metadata from over 32,000 NASA datasets (available in JSON) by looking at how keywords from the datasets are connected to title and description fields.

• Chapter 9 analyzes a dataset of Usenet messages from a diverse set of newsgroups (focused on topics like politics, hockey, technology, atheism, and more) to understand patterns across the groups.

Topics This Book Does Not Cover

This book serves as an introduction to the tidy text mining framework, along with a collection of examples, but it is far from a complete exploration of natural language processing. The CRAN Task View on Natural Language Processing provides details on other ways to use R for computational linguistics. There are several areas that you may want to explore in more detail according to your needs:

Clustering, classification, and prediction

Machine learning on text is a vast topic that could easily fill its own volume. We introduce one method of unsupervised clustering (topic modeling) in Chapter 6, but many more machine learning algorithms can be used in dealing with text.

Word embedding

One popular modern approach for text analysis is to map words to vector representations, which can then be used to examine linguistic relationships between words and to classify text. Such representations of words are not tidy in the sense that we consider here, but have found powerful applications in machine learning algorithms.

More complex tokenization

The tidytext package trusts the tokenizers package (Mullen 2016) to perform tokenization, which itself wraps a variety of tokenizers with a consistent interface, but many others exist for specific applications.

Languages other than English

Some of our users have had success applying tidytext to their text mining needs for languages other than English, but we don’t cover any such examples in this book.

About This Book

This book is focused on practical software examples and data explorations. There are few equations, but a great deal of code. We especially focus on generating real insights from the literature, news, and social media that we analyze.

We don’t assume any previous knowledge of text mining. Professional linguists and text analysts will likely find our examples elementary, though we are confident they can build on the framework for their own analyses.

We assume that the reader is at least slightly familiar with dplyr, ggplot2, and the %>% “pipe” operator in R, and is interested in applying these tools to text data. For users who don’t have this background, we recommend books such as R for Data Science by Hadley Wickham and Garrett Grolemund (O’Reilly). We believe that with a basic background and interest in tidy data, even a user early in his or her R career can understand and apply our examples.

Note

If you are reading a printed copy of this book, the images have been rendered in grayscale rather than color. To view the color versions, see the book’s GitHub page.

Conventions Used in This Book

The following typographical conventions are used in this book:

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Used for program listings, as well as within paragraphs to refer to program elements such as variable or function names, databases, data types, environment variables, statements, and keywords.

Constant width bold

Shows commands or other text that should be typed literally by the user.

Constant width italic

Shows text that should be replaced with user-supplied values or by values determined by context.

Tip

This element signifies a tip or suggestion.

Note

This element signifies a general note.

Warning

This element indicates a warning or caution.

Using Code Examples

While we show the code behind the vast majority of the analyses, in the interest of space we sometimes choose not to show the code generating a particular visualization if we’ve already provided the code for several similar graphs. We trust the reader can learn from and build on our examples, and the code used to generate the book can be found in our public GitHub repository.

This book is here to help you get your job done. In general, if example code is offered with this book, you may use it in your programs and documentation. You do not need to contact us for permission unless you’re reproducing a significant portion of the code. For example, writing a program that uses several chunks of code from this book does not require permission. Selling or distributing a CD-ROM of examples from O’Reilly books does require permission. Answering a question by citing this book and quoting example code does not require permission. Incorporating a significant amount of example code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title, author, publisher, and ISBN. For example: “Text Mining with R by Julia Silge and David Robinson (O’Reilly). Copyright 2017 Julia Silge and David Robinson, 978-1-491-98165-8.”

If you feel your use of code examples falls outside fair use or the permission given above, feel free to contact us at [e-mail].

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Acknowledgements

We are so thankful for the contributions, help, and perspectives of people who have moved us forward in this project. There are several people and organizations we would like to thank in particular.

We would like to thank Oliver Keyes and Gabriela de Queiroz for their contributions to the tidytext package, Lincoln Mullen for his work on the tokenizers package, Kenneth Benoit for his work on the quanteda package, Thomas Pedersen for his work on the ggraph package, and Hadley Wickham for his work in framing tidy data principles and building tidy tools. We would also like to thank Karthik Ram and rOpenSci, who hosted us at the unconference where we began work, and the NASA Datanauts program, for the opportunities and support they have provided Julia during her time with them.

We received thoughtful, thorough technical reviews that improved the quality of this book significantly. We would like to thank Mara Averick, Carolyn Clayton, Simon Jackson, Sean Kross, and Lincoln Mullen for their investment of time and energy in these technical reviews.

This book was written in the open, and several people contributed via pull requests or issues. Special thanks goes to those who contributed via GitHub: @ainilaha, Brian G. Barkley, Jon Calder, @eijoac, Marc Ferradou, Jonathan Gilligan, Matthew Henderson, Simon Jackson, @jedgore, @kanishkamisra, Josiah Parry, @suyi19890508, Stephen Turner, and Yihui Xie.

Finally, we want to dedicate this book to our spouses, Robert and Dana. We both could produce a great deal of sentimental text on this subject but will restrict ourselves to heartfelt thanks.