It has been twenty years since the first Harry Potter novel, the sorcerer’s/philosopher’s stone, was published. To honour the series, I started a text analysis and visualization project, which my other-half wittily dubbed Harry Plotter. In several blogs, I intend to demonstrate how Hadley Wickham’s tidyverse and packages that build on its principles, such as tidytext (free book), have taken programming in R to an all-new level. Moreover, I just enjoy making pretty graphs : )
First, we need to set up our environment in RStudio. We will be needing several packages for our analyses. Most importantly, Bradley Boehmke was nice enough to gather all Harry Potter books in his harrypotter package on GitHub. We need devtools to install that package the first time, but from then on can load it in normally. Next, we load the tidytext package, which automates and tidies a lot of the text mining functionalities. We also need plyr for a specific function (ldply()). Other tidyverse packages we can load in a single bundle, including ggplot2, dplyr, and tidyr, which I use in almost every of my projects. Finally, we load the wordcloud visualization package which draws on tm.
After loading these packages, I set some additional default options.
# LOAD IN PACKAGES # library(devtools) # devtools::install_github("bradleyboehmke/harrypotter") library(harrypotter) library(tidytext) library(plyr) library(tidyverse) library(wordcloud) # OPTIONS options(stringsAsFactors = F, # do not convert upon loading scipen = 999, # do not convert numbers to e-values max.print = 200) # stop printing after 200 values # VIZUALIZATION SETTINGS theme_set(theme_light()) # set default ggplot theme to light fs = 12 # default plot font size
With RStudio set, its time to the text of each book from the harrypotter package which we then “pipe” (%>% – another magical function from the tidyverse – specifically magrittr) along to bind all objects into a single dataframe. Here, each row represents a book with the text for each chapter stored in a separate columns. We want tidy data, so we use tidyr’s gather() function to turn each column into grouped rows. With tidytext’s unnest_tokens() function we can separate the tokens (in this case, single words) from these chapters.
# LOAD IN BOOK CHAPTERS # TRANSFORM TO TOKENIZED DATASET hp_words <- list( philosophers_stone = philosophers_stone, chamber_of_secrets = chamber_of_secrets, prisoner_of_azkaban = prisoner_of_azkaban, goblet_of_fire = goblet_of_fire, order_of_the_phoenix = order_of_the_phoenix, half_blood_prince = half_blood_prince, deathly_hallows = deathly_hallows ) %>% ldply(rbind) %>% # bind all chapter text to dataframe columns mutate(book = factor(seq_along(.id), labels = .id)) %>% # identify associated book select(-.id) %>% # remove ID column gather(key = 'chapter', value = 'text', -book) %>% # gather chapter columns to rows filter(!is.na(text)) %>% # delete the rows/chapters without text mutate(chapter = as.integer(chapter)) %>% # chapter id to numeric unnest_tokens(word, text, token = 'words') # tokenize data frame
Let’s inspect our current data format with head(), which prints the first rows (default n = 6).
# EXAMINE FIRST AND LAST WORDS OF SAGA hp_words %>% head()
## book chapter word ## 1 philosophers_stone 1 the ## 1.1 philosophers_stone 1 boy ## 1.2 philosophers_stone 1 who ## 1.3 philosophers_stone 1 lived ## 1.4 philosophers_stone 1 mr ## 1.5 philosophers_stone 1 and
A next step would be to examine word frequencies.
# PLOT WORD FREQUENCY PER BOOK hp_words %>% group_by(book, word) %>% anti_join(stop_words, by = "word") %>% # delete stopwords count() %>% # summarize count per word per book arrange(desc(n)) %>% # highest freq on top group_by(book) %>% # mutate(top = seq_along(word)) %>% # identify rank within group filter(top <= 15) %>% # retain top 15 frequent words # create barplot ggplot(aes(x = -top, fill = book)) + geom_bar(aes(y = n), stat = 'identity', col = 'black') + # make sure words are printed either in or next to bar geom_text(aes(y = ifelse(n > max(n) / 2, max(n) / 50, n + max(n) / 50), label = word), size = fs/3, hjust = "left") + theme(legend.position = 'none', # get rid of legend text = element_text(size = fs), # determine fontsize axis.text.x = element_text(angle = 45, hjust = 1, size = fs/1.5), # rotate x text axis.ticks.y = element_blank(), # remove y ticks axis.text.y = element_blank()) + # remove y text labs(y = "Word count", x = "", # add labels title = "Harry Plotter: Most frequent words throughout the saga") + facet_grid(. ~ book) + # separate plot for each book coord_flip() # flip axes
Unsuprisingly, Harry is the most common word in every single book and Ron and Hermione are also present. Dumbledore’s role as an (irresponsible) mentor becomes greater as the storyline progresses. The plot also nicely depicts other key characters:
- Lockhart and Dobby in book 2,
- Lupin in book 3,
- Moody and Crouch in book 4,
- Umbridge in book 5,
- Ginny in book 6,
- and the final confrontation with He who must not be named in book 7.
Finally, why does J.K. seem obsessively writing about eyes that look at doors?
Next, we turn to the sentiment of the text. tidytext includes three famous sentiment dictionaries:
- AFINN: including bipolar sentiment scores ranging from -5 to 5
- bing: including bipolar sentiment scores
- nrc: including sentiment scores for many different emotions (e.g., anger, joy, and surprise)
The following script identifies all words that occur both in the books and the dictionaries and combines them into a long dataframe:
# EXTRACT SENTIMENT WITH THREE DICTIONARIES hp_senti <- bind_rows( # 1 AFINN hp_words %>% inner_join(get_sentiments("afinn"), by = "word") %>% filter(score != 0) %>% # delete neutral words mutate(sentiment = ifelse(score < 0, 'negative', 'positive')) %>% # identify sentiment mutate(score = sqrt(score ^ 2)) %>% # all scores to positive group_by(book, chapter, sentiment) %>% mutate(dictionary = 'afinn'), # create dictionary identifier # 2 BING hp_words %>% inner_join(get_sentiments("bing"), by = "word") %>% group_by(book, chapter, sentiment) %>% mutate(dictionary = 'bing'), # create dictionary identifier # 3 NRC hp_words %>% inner_join(get_sentiments("nrc"), by = "word") %>% group_by(book, chapter, sentiment) %>% mutate(dictionary = 'nrc') # create dictionary identifier ) # EXAMINE FIRST SENTIMENT WORDS hp_senti %>% head()
## # A tibble: 6 x 6 ## # Groups: book, chapter, sentiment  ## book chapter word score sentiment dictionary ## ## 1 philosophers_stone 1 proud 2 positive afinn ## 2 philosophers_stone 1 perfectly 3 positive afinn ## 3 philosophers_stone 1 thank 2 positive afinn ## 4 philosophers_stone 1 strange 1 negative afinn ## 5 philosophers_stone 1 nonsense 2 negative afinn ## 6 philosophers_stone 1 big 1 positive afinn
Although wordclouds are not my favorite visualizations, they do allow for a quick display of frequencies among a large body of words.
hp_senti %>% group_by(word) %>% count() %>% # summarize count per word mutate(log_n = sqrt(n)) %>% # take root to decrease outlier impact with(wordcloud(word, log_n, max.words = 100))
It appears we need to correct for some words that occur in the sentiment dictionaries but have a different meaning in J.K. Rowling’s books. Most importantly, we need to filter two character names.
# DELETE SENTIMENT FOR CHARACTER NAMES hp_senti_sel <- hp_senti %>% filter(!word %in% c("harry","moody"))
Words per sentiment
Let’s quickly sketch the remaining words per sentiment.
# VIZUALIZE MOST FREQUENT WORDS PER SENTIMENT hp_senti_sel %>% # NAMES EXCLUDED group_by(word, sentiment) %>% count() %>% # summarize count per word per sentiment group_by(sentiment) %>% arrange(sentiment, desc(n)) %>% # most frequent on top mutate(top = seq_along(word)) %>% # identify rank within group filter(top <= 15) %>% # keep top 15 frequent words ggplot(aes(x = -top, fill = factor(sentiment))) + # create barplot geom_bar(aes(y = n), stat = 'identity', col = 'black') + # make sure words are printed either in or next to bar geom_text(aes(y = ifelse(n > max(n) / 2, max(n) / 50, n + max(n) / 50), label = word), size = fs/3, hjust = "left") + theme(legend.position = 'none', # remove legend text = element_text(size = fs), # determine fontsize axis.text.x = element_text(angle = 45, hjust = 1), # rotate x text axis.ticks.y = element_blank(), # remove y ticks axis.text.y = element_blank()) + # remove y text labs(y = "Word count", x = "", # add manual labels title = "Harry Plotter: Words carrying sentiment as counted throughout the saga", subtitle = "Using tidytext and the AFINN, bing, and nrc sentiment dictionaries") + facet_grid(. ~ sentiment) + # separate plot for each sentiment coord_flip() # flip axes
This seems ok. Let’s continue to plot the sentiment over time.
Positive and negative sentiment throughout the series
As positive and negative sentiment is included in each of the three dictionaries we can to compare and contrast scores.
# VIZUALIZE POSTIVE/NEGATIVE SENTIMENT OVER TIME plot_sentiment <- hp_senti_sel %>% # NAMES EXCLUDED group_by(dictionary, sentiment, book, chapter) %>% summarize(score = sum(score), # summarize AFINN scores count = n(), # summarize bing and nrc counts # move bing and nrc counts to score score = ifelse(is.na(score), count, score)) %>% filter(sentiment %in% c('positive','negative')) %>% # only retain bipolar sentiment mutate(score = ifelse(sentiment == 'negative', -score, score)) %>% # reverse negative values # create area plot ggplot(aes(x = chapter, y = score)) + geom_area(aes(fill = score > 0),stat = 'identity') + scale_fill_manual(values = c('red','green')) + # change colors # add black smoothed line without standard error geom_smooth(method = "loess", se = F, col = "black") + theme(legend.position = 'none', # remove legend text = element_text(size = fs)) + # change font size labs(x = "Chapter", y = "Sentiment score", # add labels title = "Harry Plotter: Sentiment during the saga", subtitle = "Using tidytext and the AFINN, bing, and nrc sentiment dictionaries") + # separate plot per book and dictionary and free up x-axes facet_grid(dictionary ~ book, scale = "free_x") plot_sentiment
Let’s zoom in on the smoothed average.
plot_sentiment + coord_cartesian(ylim = c(-100,50)) # zoom in plot
Sentiment seems overly negative throughout the series. Particularly salient is that every book ends on a down note, except the Prisoner of Azkaban. Moreover, sentiment becomes more volatile in books four through six. These start out negative, brighten up in the middle, just to end in misery again. In her final book, J.K. Rowling depicts a world about to be conquered by the Dark Lord and the average negative sentiment clearly resembles this grim outlook.
The bing sentiment dictionary estimates the most negative sentiment on average, but that might be due to this specific text.
Other emotions throughout the series
Finally, let’s look at the other emotions that are included in the nrc dictionary.
# VIZUALIZE EMOTIONAL SENTIMENT OVER TIME hp_senti_sel %>% # NAMES EXCLUDED filter(!sentiment %in% c('negative','positive')) %>% # only retain other sentiments (nrc) group_by(sentiment, book, chapter) %>% count() %>% # summarize count # create area plot ggplot(aes(x = chapter, y = n)) + geom_area(aes(fill = sentiment), stat = 'identity') + # add black smoothing line without standard error geom_smooth(aes(fill = sentiment), method = "loess", se = F, col = 'black') + theme(legend.position = 'none', # remove legend text = element_text(size = fs)) + # change font size labs(x = "Chapter", y = "Emotion score", # add labels title = "Harry Plotter: Emotions during the saga", subtitle = "Using tidytext and the nrc sentiment dictionary") + # separate plots per sentiment and book and free up x-axes facet_grid(sentiment ~ book, scale = "free_x")
This plot is less insightful as either the eight emotions are represented by similar words or J.K. Rowling combines all in her writing simultaneously. Patterns across emotions are highly similar, evidenced especially by the patterns in the Chamber of Secrets. In a next post, I will examine sentiment in a more detailed fashion, testing the differences over time and between characters statistically. For now, I hope you enjoyed these visualizations. Feel free to come back or subscribe to read my subsequent analyses.
The second blog in the Harry Plotter series examines the stereotypes behind the Hogwarts houses.