In this vignette, the utility of the package is illustrated by showing how it can be used to study a corpus consisting of every State of the Union Address made by a United States president through 2016. It highlights some of the major benefits of the tidy datamodel as it applies to the study of textual data, though by no means attempts to give an exhaustive coverage of all the available tables and approaches. The examples make heavy use of the table verbs provided by dplyr, the piping notation of magrittr and ggplot2 graphics. These are used because they best illustrate the advantages of the tidy data model that has been built in cleanNLP for representing corpus annotations.
Exploratory Analysis
Simple summary statistics are easily computed from the table of tokens. To see the distribution of sentence length, the token table is grouped by the document and sentence id and the number of rows within each group are computed. The percentiles of these counts give a quick summary of the distribution.
anno$token %>%
group_by(doc_id, sid) %>%
summarize(sent_len = n()) %$%
quantile(sent_len, seq(0,1,0.1))
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
1 9 14 18 22 26 30 35 42 55 398
The median sentence has 26 tokens, whereas at least one has over 600 (this is due to a bulleted list in one of the written addresses being treated as a single sentence) To see the most frequently used nouns in the dataset, the token table is filtered on the universal part of speech field, grouped by lemma, and the number of rows in each group are once again calculated. Sorting the output and selecting the top \(42\) nouns, yields a high level summary of the topics of interest within this corpus.
anno$token %>%
filter(upos == "NOUN") %>%
group_by(lemma) %>%
summarize(count = n()) %>%
top_n(n = 42, count) %>%
arrange(desc(count)) %>%
use_series(lemma)
[1] "year" "country" "people" "law"
[5] "nation" "time" "government" "power"
[9] "interest" "world" "war" "citizen"
[13] "service" "part" "duty" "system"
[17] "peace" "right" "state" "man"
[21] "program" "policy" "work" "condition"
[25] "legislation" "act" "force" "subject"
[29] "effort" "purpose" "treaty" "business"
[33] "land" "action" "measure" "way"
[37] "question" "relation" "consideration" "attention"
[41] "report" "life"
The result is generally as would be expected from a corpus of government speeches, with references to proper nouns representing various organizations within the government and non-proper nouns indicating general topics of interest such as “country”, “law”, and “peace”.
The length in tokens of each address is calculated similarly by grouping and summarizing at the document id level. The results can be joined with the document table to get the year of the speech and then piped in a ggplot2 command to illustrate how the length of the State of the Union has changed over time.
anno$token %>%
group_by(doc_id) %>%
summarize(n = n()) %>%
left_join(anno$document, by="doc_id") %>%
ggplot(aes(year, n)) +
geom_line(color = grey(0.8)) +
geom_point(aes(color = sotu_type)) +
geom_smooth(method="loess", formula = y ~ x) +
theme_minimal()
Here, color is used to represent whether the address was given as an oral address or a written document. The output shows that their are certainly time trends to the address length, with the form of the address (written versus spoken) also having a large effect on document length.
Finding the most used entities from the entity table over the time period of the corpus yields an alternative way to see the underlying topics. A slightly modified version of the code snippet used to find the top nouns in the dataset can be used to find the top entities.
anno$entity %>%
filter(entity_type == "LOC") %>%
group_by(entity) %>%
summarize(count = n()) %>%
top_n(n = 44, count) %>%
arrange(desc(count)) %>%
use_series(entity)
[1] "Europe" "Pacific" "Asia"
[4] "Atlantic" "Africa" "Territories"
[7] "the Middle East" "Central America" "South"
[10] "West" "earth" "Mississippi"
[13] "Earth" "Latin America" "South America"
[16] "East" "Mediterranean" "the Gulf of Mexico"
[19] "the Southern States" "Western Europe" "North"
[22] "the Pacific Ocean" "the Rocky Mountains" "Americas"
[25] "the Western Hemisphere" "the Far East" "the Mississippi River"
[28] "Gulf" "the Persian Gulf" "Middle East"
[31] "Prussia" "Caribbean" "Eastern Europe"
[34] "Southeast Asia" "Lake Erie" "North America"
[37] "the Pacific Coast" "the Northern States" "Bering Sea"
[40] "District" "the Near East" "the west coast"
[43] "the West Indies" "South Asia" "Southwest Asia"
[46] "the Bering Sea" "West Point"
The ability to redo analyses from a slightly different perspective is a direct consequence of the tidy data model supplied by cleanNLP.
The top locations include some obvious and some less obvious instances. Those sovereign nations included such as Great Britain, Mexico, Germany, and Japan seem as expected given either the United State’s close ties or periods of war with them. The top states include the most populous regions but also smaller states.
One of the most straightforward way of extracting a high-level summary of the content of a speech is to extract all direct object object dependencies where the target noun is not a very common word. In order to do this for a particular speech, the dependency table is joined to the document table, a particular document is selected, and relationships of type “dobj” (direct object) are filtered out. The result is then joined to the data set word_frequency, which is included with cleanNLP, and pairs with a target occurring less than 0.5% of the time are selected to give the final result. Here is an example of this using the first address made by George W. Bush in 2001:
anno$token %>%
left_join(
anno$token,
c("doc_id"="doc_id", "sid"="sid", "tid"="tid_source"),
suffix=c("", "_source")
) %>%
left_join(anno$document, by="doc_id") %>%
filter(year == 2001) %>%
filter(relation == "dobj") %>%
select(doc_id = doc_id, start = token, word = token_source) %>%
left_join(word_frequency, by="word") %>%
filter(frequency < 0.001) %>%
select(doc_id, start, word) %$%
sprintf("%s => %s", start, word)
[1] "signs => layoffs" "amount => unprecedented"
[3] "effort => recruit" "care => lawsuits"
[5] "approach => hopeful" "poor => disadvantaged"
[7] "meal => mentor" "action => compassionate"
[9] "dollars => trillion" "marriage => discourage"
[11] "strategy => confront" "people => allies"
[13] "defenses => missile" "ourselves => allies"
[15] "ability => negotiate"
Most of these phrases correspond with the “compassionate conservatism” that George W. Bush ran under in the preceding 2000 election. Applying the same analysis to the 2002 State of the Union, which came under the shadow of the September 11th terrorist attacks, shows a drastic shift in focus.
anno$token %>%
left_join(
anno$token, c("doc_id"="doc_id", "sid"="sid", "tid"="tid_source"),
suffix=c("", "_source")
) %>%
left_join(anno$document, by="doc_id") %>%
filter(year == 2002) %>%
filter(relation == "dobj") %>%
select(doc_id = doc_id, start = token, word = token_source) %>%
left_join(word_frequency, by="word") %>%
filter(frequency < 0.001) %>%
select(doc_id, start, word) %$%
sprintf("%s => %s", start, word)
[1] "dangers => unprecedented" "debt => owe"
[3] "terrorists => regimes" "terrorists => plotting"
[5] "parasites => threaten" "gas => poison"
[7] "defenses => missile" "America => allies"
[9] "America => allies" "police => heroic"
[11] "police => firefighters" "arrivals => departures"
[13] "neighborhoods => safer" "package => stimulus"
[15] "ethic => creed" "best => emerged"
[17] "doctors => mobilized" "efforts => recruit"
[19] "peace => prosperity" "freedom => dignity"
Here the topics have almost entirely shifted to counter-terrorism and national security efforts.
Models
Principal Component Analysis (PCA)
The cnlp_utils_tfidf function provided by cleanNLP converts a token table into a sparse matrix representing the term-frequency inverse document frequency matrix (or any intermediate part of that calculation). This is particularly useful when building models from a textual corpus. The cnlp_utils_pca, also included with the package, takes a matrix and returns a data frame containing the desired number of principal components. Dimension reduction involves piping the token table for a corpus into the cnlp_utils_tfidf function and passing the results to cnlp_utils_pca.
pca <- anno$token %>%
filter(xpos %in% c("NN", "NNS")) %>%
cnlp_utils_tfidf(min_df = 0.05, max_df = 0.95, tf_weight = "dnorm") %>%
cnlp_utils_pca()
pca <- bind_cols(anno$document, pca)
pca
# A tibble: 236 x 8
president year years_active party sotu_type doc_id PC1 PC2
<chr> <int> <chr> <chr> <chr> <int> <dbl> <dbl>
1 George Washington 1790 1789-1793 Nonpartis… speech 1 -2.30 13.0
2 George Washington 1790 1789-1793 Nonpartis… speech 2 -4.37 16.5
3 George Washington 1791 1789-1793 Nonpartis… speech 3 -5.48 12.8
4 George Washington 1792 1789-1793 Nonpartis… speech 4 -3.54 12.1
5 George Washington 1793 1793-1797 Nonpartis… speech 5 -16.8 18.8
6 George Washington 1794 1793-1797 Nonpartis… speech 6 -5.98 13.6
7 George Washington 1795 1793-1797 Nonpartis… speech 7 -12.7 20.6
8 George Washington 1796 1793-1797 Nonpartis… speech 8 -8.98 12.6
9 John Adams 1797 1797-1801 Federalist speech 9 -1.19 10.9
10 John Adams 1798 1797-1801 Federalist speech 10 -5.54 13.0
# … with 226 more rows
In this example only non-proper nouns have been included in order to minimize the stylistic attributes of the speeches in order to focus more on their content. We can draw a scatter plot of the speeches using these components to see a definitive temporal pattern to the documents, with the 20th century addresses forming a distinct cluster on the right side of the plot.
ggplot(pca, aes(PC1, PC2)) +
geom_point(aes(color = cut(year, 10, dig.lab = 4)), alpha = 0.35, size = 4) +
ggrepel::geom_text_repel(data = filter(pca, !duplicated(president)),
aes(label = president), color = grey(0.4), cex = 3) +
labs(color = "Years") +
scale_color_viridis_d(end = 0.9, option = "C") +
theme(axis.title.x = element_text(size = 14),
axis.title.y = element_text(size = 14),
axis.text.x = element_blank(),
axis.text.y = element_blank()) +
theme_void()
Topic Models (LDA)
The output of the cnlp_utils_tf function (it calls cnlp_utils_tfidf with different default parameters to yield raw term frequencies) may be given directly to the LDA function in the package topicmodels.
library(topicmodels)
mat <- anno$token %>%
filter(xpos %in% c("NN", "NNS")) %>%
cnlp_utils_tf(min_df = 0.05, max_df = 0.95)
tm <- LDA(mat, k = 16)
The topics, ordered by approximate time period, are visualized below:
terms <- posterior(tm)$terms
topics <- posterior(tm)$topics
topic_df <- tibble(topic = as.integer(col(topics)),
doc_id = anno$document$doc_id[as.integer(row(topics))],
val = as.numeric(topics)) %>%
left_join(anno$document, by="doc_id")
top_terms <- apply(terms, 1,
function(v) {
paste(colnames(mat)[order(v, decreasing = TRUE)[1:5]], collapse = ", ")
})
top_terms <- as.character(top_terms)
index <- rank(-1 * tapply(topic_df$year * topic_df$val, topic_df$topic, which.max))
topic_df$topic_new <- index[topic_df$topic]
top_terms_df <- tibble(top_terms, topic = 1:length(top_terms))
top_terms_df$topic_new <- index[top_terms_df$topic]
ggplot(topic_df, aes(year, topic_new)) +
geom_point(aes(size = val, color = factor(topic_new))) +
geom_text(data = top_terms_df, x = mean(topic_df$year),
size = 5, aes(y = topic_new + 0.4, label = top_terms, color = factor(topic_new)),
show.legend = FALSE) +
scale_color_viridis_d(end = 0.7, option = "C") +
theme(axis.text.y=element_blank(),
axis.title.y=element_blank(),
legend.position="bottom",
axis.title.x = element_text(size = 16),
axis.text.x = element_text(size = 14)) +
labs(size = "Posterior probability") +
theme_minimal() +
scale_y_continuous(breaks=FALSE) +
ylab("") +
xlab("Year") +
guides(colour = FALSE)
Most topics persist for a few decades and then largely disappear, though some persist over non-contiguous periods of the presidency. The Energy topic, for example, appears during the 1950s and crops up again during the energy crisis of the 1970s. The “world, man, freedom, force, defense” topic peaks during both World Wars, but is absent during the 1920s and early 1930s.
Predictive Models
Finally, the cleanNLP data model is also convenient for building predictive models. The State of the Union corpus does not lend itself to an obviously applicable prediction problem. A classifier that distinguishes speeches made by George W. Bush and Barrack Obama will be constructed here for the purpose of illustration.
As a first step, a term-frequency matrix is extracted using the same technique as was used with the topic modeling function. However, here the frequency is computed for each sentence in the corpus rather than the document as a whole.
df <- anno$token %>%
left_join(anno$document, by="doc_id") %>%
filter(year > 2000) %>%
mutate(new_id = paste(doc_id, sid, sep = "-")) %>%
filter(xpos %in% c("NN", "NNS"))
mat <- cnlp_utils_tf(df, doc_var = "new_id")
dim(mat)
[1] 4938 2349
It will be necessary to define a response variable y indicating whether this is a speech made by President Obama as well as a training flag indicating which speeches were made in odd numbered years. This is done via a separate table join and a pair of mutations.
meta <- tibble(new_id = rownames(mat)) %>%
left_join(df[!duplicated(df$new_id),], by="new_id") %>%
mutate(y = as.numeric(president == "Barack Obama")) %>%
mutate(train = year %in% seq(2001, 2016, by = 2))
The output may now be used as input to the elastic net function provided by the glmnet package. The response is set to the binomial family given the binary nature of the response and training is done on only those speeches occurring in odd-numbered years. Cross-validation is used in order to select the best value of the model’s tuning parameter.
library(glmnet)
model <- cv.glmnet(mat[meta$train,], meta$y[meta$train], family = "binomial")
A boxplot of the predicted classes for each address is given below:
meta$pred <- predict(model, newx = mat, type = "response", s = model$lambda.1se)
ggplot(meta, aes(factor(year),pred)) +
geom_boxplot(aes(fill = relevel(factor(president), "George W. Bush"))) +
labs(fill = "President") + xlab("year") + ylab("predicted probability") +
scale_fill_viridis_d(alpha = 0.6, end = 0.75, option = "C") +
coord_flip() +
theme(axis.title.x = element_text(size = 12),
axis.text.x = element_text(size = 10),
axis.title.y = element_text(size = 12),
axis.text.y = element_text(size = 10)) +
theme_minimal() +
ylab("Predicted probability") +
xlab("Year")
The algorithm does a very good job of separating the speeches. Looking at the odd years versus even years (the training and testing sets, respectively) indicates that the model has not been over-fit.
One benefit of the penalized linear regression model is that it is possible to interpret the coefficients in a meaningful way. Here are the non-zero elements of the regression vector, coded as whether the have a positive (more Obama) or negative (more Bush) sign:
beta <- coef(model, s = model[["lambda"]][11])[-1]
sprintf("%s (%d)", colnames(mat), sign(beta))[beta != 0]
[1] "job (1)" "business (1)" "family (1)" "citizen (-1)"
[5] "terrorist (-1)" "freedom (-1)" "education (1)" "home (1)"
[9] "college (1)" "weapon (-1)" "deficit (1)" "company (1)"
[13] "enemy (-1)" "peace (-1)" "terror (-1)" "hope (-1)"
[17] "income (-1)" "drug (-1)" "kid (1)" "regime (-1)"
[21] "class (1)" "crisis (1)" "industry (1)" "need (-1)"
[25] "fact (1)" "relief (-1)" "bank (1)" "liberty (-1)"
[29] "funding (-1)" "society (-1)" "account (-1)" "cause (-1)"
[33] "folk (1)" "duty (-1)" "compassion (-1)" "supply (-1)"
[37] "environment (-1)" "inspector (-1)"
These generally seem as expected given the main policy topics of focus under each administration. During most of the Bush presidency, as mentioned before, the focus was on national security and foreign policy. Obama, on the other hand, inherited the recession of 2008 and was far more focused on the overall economic policy.