---
title: "Text Mining with gutenbergr and tidytext"
description: >
  An introduction to text mining with tidytext and gutenbergr using Jane Austen's "Persuasion"
output:
  rmarkdown::html_vignette:
    toc: true
vignette: >
  %\VignetteIndexEntry{Text Mining with gutenbergr and tidytext}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(
  collapse = FALSE,
  comment = "#>",
  fig.width = 7,
  fig.height = 6,
  fig.path = "../man/figures/",
  warning = FALSE,
  message = FALSE
)
```

This vignette demonstrates a complete text mining workflow using gutenbergr and [tidytext](https://github.com/juliasilge/tidytext). We'll perform an in-depth analysis of Jane Austen's *Persuasion*, exploring its vocabulary, sentiment, structure, and themes. See [_Text Mining with R_](https://www.tidytextmining.com/) for a great introduction to text mining.

## Required Libraries

```{r windows-check, include=FALSE}
tryCatch(
  library(gutenbergr),
  error = function(e) {
    # Fallback for Windows check environments
    devtools::load_all("..")
  }
)
```

```{r packages}
library(dplyr)
library(tidytext)
library(ggplot2)
library(tidyr)
library(stringr)
```

## Download the Book

First, let's find and download Jane Austen's *Persuasion*:

```{r find-book}
gutenberg_works(str_detect(title, "Persuasion"))
```

We can see there are multiple works returned. 105 is *Persuasion*, so let's download that:

```{r download, eval=FALSE}
persuasion <- gutenberg_download(105, meta_fields = "title")
```

```{r download-sample, echo=FALSE}
# For vignette building, use sample data
persuasion <- gutenbergr::sample_books |>
  filter(gutenberg_id == 105) |>
  select(gutenberg_id, text, title)
```

```{r show-book}
persuasion
```

## Structural Analysis: Adding Chapters

Project Gutenberg texts processed into tibbles of lines. To analyze the book's progression, we use `gutenberg_add_sections()`. This function identifies headers and fills them down to create a structural column.

```{r sections}
persuasion <- persuasion |>
  gutenberg_add_sections(
    pattern = "^Chapter [IVXLCDM]+",
    section_col = "chapter",
    format_fn = function(x) {
      x |>
        str_remove("^CHAPTER\\s+") |>
        str_remove("\\.$") |>
        as.roman() |>
        as.numeric()
    }
  )

# Preview the new structure
persuasion |>
  filter(!is.na(chapter)) |>
  head()
```

## Tokenization

We need to move from a one-row-per-line format to a one-row-per-token format. We'll use `tidytext::unnest_tokens()` to split the text into individual words and remove stop words `tidytext::stop_words`.

```{r tokenize}
words <- persuasion |>
  unnest_tokens(word, text) |>
  anti_join(stop_words, by = "word")
```

## Word Frequency Analysis

Tokenization makes it trivial to find the most frequent words in the text:

```{r word-frequency}
word_counts <- words |>
  count(word, sort = TRUE)

word_counts
```

Let's visualize the top 20 words:

```{r top-words, fig.alt="Horizontal bar chart showing the 20 most frequent words in Persuasion after removing stop words."}
word_counts |>
  slice_max(n, n = 20) |>
  mutate(word = reorder(word, n)) |>
  ggplot(aes(x = n, y = word, fill = word)) +
  geom_col(show.legend = FALSE) +
  labs(
    title = expression(paste("Most Common Words in ", italic("Persuasion"))),
    x = "Frequency",
    y = NULL
  ) +
  theme_minimal()
```

Character names (Anne, Captain, Elliot, Wentworth) dominate the most frequent words, which makes sense for a character-driven novel.

## Sentiment Analysis

Natural language processing uses sentiment analysis to identify emotive/affective states.

### Overall Sentiment

Let's use the [NRC sentiment lexicon](https://saifmohammad.com/WebPages/NRC-Emotion-Lexicon.htm), which classifies words into categories like "joy", "trust", "fear", and "sadness". This will allow us to view the overall sentiment of the book.

> Note: The NRC lexicon requires accepting a license agreement during installation and is only free for non-commercial use. The code below shows the analysis workflow, with pre-computed results displayed.

```{r sentiment-nrc, eval=FALSE}
nrc_sentiments <- get_sentiments("nrc")

word_sentiments <- words |>
  inner_join(nrc_sentiments, by = "word", relationship = "many-to-many") |>
  count(sentiment, sort = TRUE)
```

Visualize the distribution of sentiments:

```{r sentiment-plot, eval=FALSE}
word_sentiments |>
  mutate(sentiment = reorder(sentiment, n)) |>
  ggplot(aes(x = n, y = sentiment, fill = sentiment)) +
  geom_col(show.legend = FALSE) +
  labs(
    title = expression(paste(
      "Sentiment Distribution in ",
      italic("Persuasion")
    )),
    x = "Word Count",
    y = NULL
  ) +
  theme_minimal()
```

![Sentiment distribution in Persuasion](../man/figures/sentiment-plot-1.png)

### By Chapter

We can aggregate these sentiments by the chapter structure we created earlier.

```{r nrc-chapters, eval=FALSE}
nrc_by_chapter <- words |>
  inner_join(nrc_sentiments, by = "word", relationship = "many-to-many") |>
  count(chapter, sentiment) |>
  filter(!is.na(chapter))

nrc_by_chapter |>
  filter(sentiment %in% c("joy", "sadness", "anger", "fear")) |>
  ggplot(aes(x = chapter, y = n, fill = factor(sentiment))) +
  geom_col(show.legend = FALSE) +
  facet_wrap(~sentiment, ncol = 2, scales = "free_y") +
  labs(
    title = expression(paste("Sentiment by Chapter in ", italic("Persuasion"))),
    x = "Chapter",
    y = "Word Count"
  ) +
  theme_minimal() +
  theme(
    axis.text.x = element_text(angle = 45, hjust = 1),
    strip.text = element_text(face = "bold")
  )
```

![Sentiment by chapter in Persuasion](../man/figures/nrc-chapters-1.png)

### Sentiment Progression

We can also see the general emotive content as the book progresses by dividing the text into "bins" of 500 words to track how specific emotions fluctuate across the narrative arc.

For good measure, let's add another x-axis with chapter labels so we can correlate the sentiment with portions of the narrative.

```{r nrc-bins, eval=FALSE}
# Add a running index to preserve order and calculate bins
words_with_index <- words |>
  mutate(word_index = row_number()) |>
  mutate(bin = (word_index - 1) %/% 500 + 1)

nrc_binned <- words_with_index |>
  inner_join(nrc_sentiments, by = "word", relationship = "many-to-many") |>
  count(bin, sentiment)

# Add labels for chapters
chapter_breaks <- words |>
  filter(!is.na(chapter)) |>
  mutate(word_index = row_number()) |>
  group_by(chapter) |>
  slice_min(word_index, n = 1) |>
  ungroup() |>
  mutate(
    bin = (word_index - 1) %/% 500 + 1
  ) |>
  filter(chapter %% 2 == 0)

nrc_binned |>
  filter(sentiment %in% c("joy", "sadness", "anger", "fear")) |>
  ggplot(aes(x = bin, y = n, color = sentiment)) +
  geom_line(linewidth = 1, show.legend = FALSE) +
  facet_wrap(~sentiment, ncol = 2, scales = "free_y") +
  scale_x_continuous(
    name = "Word Bin (500 words)",
    sec.axis = sec_axis(
      ~.,
      breaks = chapter_breaks$bin,
      labels = chapter_breaks$chapter,
      name = "Chapter"
    )
  ) +
  labs(
    title = expression(paste(
      "Sentiment Progression in ",
      italic("Persuasion")
    )),
    subtitle = "NRC sentiments by word bin with chapter reference",
    y = "Word Count"
  ) +
  theme_minimal()
```

![Sentiment progression in Persuasion](../man/figures/nrc-bins-1.png)

## TF-IDF: Finding Unique Chapter Words

While simple frequency tells us who the main characters are, TF-IDF, or term frequency–inverse document frequency, tells us which words are most important to a specific chapter relative to the rest of the corpus. This is excellent for identifying specific plot points or settings (like the move to Bath or the trip to Lyme).

```{r tf-idf}
chapter_words <- persuasion |>
  unnest_tokens(word, text) |>
  count(chapter, word, sort = TRUE) |>
  bind_tf_idf(word, chapter, n)

# Look at the most "important" words for chapters 10 through 13
chapter_words |>
  filter(chapter %in% 10:13) |>
  group_by(chapter) |>
  slice_max(tf_idf, n = 5) |>
  ungroup() |>
  mutate(word = reorder(word, tf_idf)) |>
  ggplot(aes(tf_idf, word, fill = factor(chapter))) +
  geom_col(show.legend = FALSE) +
  facet_wrap(~chapter, scales = "free") +
  labs(
    title = "Highest TF-IDF words in Chapters 10-13",
    x = "TF-IDF",
    y = NULL
  ) +
  theme_minimal()
```