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 [@R-tidytext] 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 of 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.
1.1 What is tidy text?
As described by Hadley Wickham [@tidydata], tidy data has a specific structure:
- Each variable is a column
- Each observation is a row
- Each type of observational unit is a table
We thus define the tidy text format as being a table with one-token-per-row. A token is a meaningful unit of text, such as a word, that we are interested in using for analysis, and tokenization is the process of splitting text into tokens. This one-token-per-row structure is in contrast to the ways text is often stored in current analyses, as strings, in a structured “corpus” object, or in a document-term matrix. For tidy text mining, the token that is stored in each row is most often a single word, but can also be an n-gram, sentence, or paragraph. In the tidytext package, we provide functionality to tokenize by commonly used units of text like these and convert to a one-term-per-row format.
Tidy data sets allow manipulation with a standard set of “tidy” tools, including popular packages such as dplyr [@R-dplyr], tidyr [@R-tidyr], ggplot2 [@R-ggplot2], and broom [@R-broom]. By keeping the input and output in tidy tables, users can transition fluidly between these packages. We’ve found these tidy tools extend naturally to many text analyses and explorations.
At the same time, the tidytext package doesn’t expect a user to keep text data in a tidy form at all times during an analysis. The package includes functions to
tidy() objects (see the broom package [Robinson et al cited above]) from popular text mining R packages such as tm [@tm] and quanteda [@R-quanteda]. This allows, for example, a workflow where importing, filtering, and processing is done using dplyr and other tidy tools, after which the data is converted into a document-term matrix for machine learning applications. The models can then be re-converted into a tidy form for interpretation and visualization with ggplot2.
1.2 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 do 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. We believe that with a basic background and interest in tidy data, even a user early in their R career can understand and apply our 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.
We start by introducing the tidy text format, and some of the ways dplyr, tidyr, and tidytext allow informative analyses of this structure.
- Chapter 2 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 3 shows how to perform sentiment analysis on a tidy text dataset, using the
sentimentsdataset from tidytext and
- Chapter 4 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 5 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 non-tidy formats.
- Chapter 6 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 7 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 8 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 9 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 10 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.
1.4 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 7 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 [@R-tokenizers] 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.
We feel that the tidy data philosphy is a powerful tool to make handling data easier and more effective, and this is no less true when it comes to handling text. We also believe tidy tools are well suited to extensions beyond the methods and examples we provide here.
We are so thankful for the contributions, help, and perspective 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 Gabriela de Queiroz for her contributions to the package while we were at the unconference where we began work on the tidytext package, Lincoln Mullen for his work on tokenizers, Kenneth Benoit for his work on the quanteda package, Thomas Pedersen for his work on ggraph, and Hadley Wickham for his work in framing tidy data principles and building tidy tools. We would also like to thank rOpenSci, which 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.