options(width = 1000) knitr::opts_chunk$set(echo = TRUE, message = FALSE, warning = FALSE, comment = NA, eval = (require(topicmodels)))
In order to get the most out of the package, we will show how to use the outcome of the annotation to improve topic modelling. The main use cases of using the outcome of the annotation is to
Let's show this.
Let's start by annotating some text in French. The annotated data.frame can next be used for basic text analytics.
library(udpipe) ud_model <- udpipe_download_model(language = "french")
knitr::opts_chunk$set(echo = TRUE, message = FALSE, warning = FALSE, comment = NA, eval = !ud_model$download_failed)
data(brussels_reviews) comments <- subset(brussels_reviews, language %in% "fr") ud_model <- udpipe_load_model(ud_model$file_model) x <- udpipe_annotate(ud_model, x = comments$feedback, doc_id = comments$id) x <- as.data.frame(x)
The resulting data.frame has a field called upos
which is the Universal Parts of Speech tag and also a field called lemma
which is the root form of each token in the text. These 2 fields give us a broad range of topic modelling possibilities.
str(x)
You can easily go from this annotated data.frame to a document-term-matrix which is used by a lot of other text mining R packages. In this case, we will build topics at the sentence level.
The advantage of this package over other packages is that
Below we fit a topic model on the nouns only.
## Define the identifier at which we will build a topic model x$topic_level_id <- unique_identifier(x, fields = c("doc_id", "paragraph_id", "sentence_id")) ## Get a data.frame with 1 row per id/lemma dtf <- subset(x, upos %in% c("NOUN")) dtf <- document_term_frequencies(dtf, document = "topic_level_id", term = "lemma") head(dtf) ## Create a document/term/matrix for building a topic model dtm <- document_term_matrix(x = dtf) ## Remove words which do not occur that much dtm_clean <- dtm_remove_lowfreq(dtm, minfreq = 5) head(dtm_colsums(dtm_clean)) ## Remove nouns which you really do not like (mostly too common nouns) dtm_clean <- dtm_remove_terms(dtm_clean, terms = c("appartement", "appart", "eter")) ## Or keep of these nouns the top 50 based on mean term-frequency-inverse document frequency dtm_clean <- dtm_remove_tfidf(dtm_clean, top = 50)
Once we have our document/term/matrix, topic modelling is simple
library(topicmodels) m <- LDA(dtm_clean, k = 4, method = "Gibbs", control = list(nstart = 5, burnin = 2000, best = TRUE, seed = 1:5))
Furthermore, we can also easily use the model to predict to which topic a new document belongs to. And the predict function will give correctly NA values for documents for which we don't have terms which are used in the model which is a pain in other R packages. It also allows to provide labels to each topic and gives the difference in topic probability to the next best topic which is usefull to see how clear-cut your topics are.
scores <- predict(m, newdata = dtm, type = "topics", labels = c("labela", "labelb", "labelc", "xyz")) str(scores)
To interpret the topic model and to give appropriate labels, you can get the most emitted terms for each topic with a minimal term emittance probability and the minimum number of terms to show. It is also usefull to look at the textrank package (https://CRAN.R-project.org/package=textrank) which allows to summarise text and can be used to find the most relevant sentences within each topic.
predict(m, type = "terms", min_posterior = 0.05, min_terms = 3)
If you want to do the same on adjectives + nouns, just change the above code where it says upos %in% c("NOUN")
in upos %in% c("NOUN", "ADJ")
and you are ready.
## Build document term matrix on nouns/adjectives only dtf <- subset(x, upos %in% c("NOUN", "ADJ") & !lemma %in% c("appartement", "appart", "eter", "tres")) dtf <- document_term_frequencies(dtf, document = "topic_level_id", term = "lemma") dtm <- document_term_matrix(x = dtf) dtm_clean <- dtm_remove_lowfreq(dtm, minfreq = 5) ## Build topic model + get topic terminology m <- LDA(dtm_clean, k = 4, method = "Gibbs", control = list(nstart = 5, burnin = 2000, best = TRUE, seed = 1:5)) topicterminology <- predict(m, type = "terms", min_posterior = 0.025, min_terms = 5) scores <- predict(m, newdata = dtm, type = "topics")
Once you have topics, visualising these can also be easily done with the igraph and ggraph packages. Below one possible plot is shown. It shows for a certain topic the co-occurrence of terms
library(igraph) library(ggraph) library(ggplot2) x_topics <- merge(x, scores, by.x="topic_level_id", by.y="doc_id") wordnetwork <- subset(x_topics, topic %in% 1 & lemma %in% topicterminology[[1]]$term) wordnetwork <- cooccurrence(wordnetwork, group = c("topic_level_id"), term = "lemma") wordnetwork <- graph_from_data_frame(wordnetwork) ggraph(wordnetwork, layout = "fr") + geom_edge_link(aes(width = cooc, edge_alpha = cooc), edge_colour = "pink") + geom_node_text(aes(label = name), col = "darkgreen", size = 4) + theme_graph(base_family = "Arial Narrow") + labs(title = "Words in topic 1 ", subtitle = "Nouns & Adjective cooccurrence")
Another possibility is showing correlations among the terms driving the topic for only documents of that topic.
topicterminology <- predict(m, type = "terms", min_posterior = 0.05, min_terms = 10) termcorrs <- subset(x_topics, topic %in% 1 & lemma %in% topicterminology[[1]]$term) termcorrs <- document_term_frequencies(termcorrs, document = "topic_level_id", term = "lemma") termcorrs <- document_term_matrix(termcorrs) termcorrs <- dtm_cor(termcorrs) termcorrs[lower.tri(termcorrs)] <- NA diag(termcorrs) <- NA library(qgraph) qgraph(termcorrs, layout = "spring", labels = colnames(termcorrs), directed = FALSE, borders = FALSE, label.scale = FALSE, label.cex = 1, node.width = 0.5)
You mostly get better, more interpretable results in topic models if you include compound keywords in the model. Let's show the steps how you can accomplish this.
keywords_rake
, keywords_phrases
, keywords_collocation
functions or with functionality from the textrank R package.txt_recode_ngram
to recode words to keywords. This will replace a sequence of words with its compound multi-word expression by first starting with words which contain more terms.In the below example, we are building a topic model on all nouns, all compound keywords which consists of nouns and adjectives and on all identified noun phrases.
## Find keywords with RAKE keyw_rake <- keywords_rake(x, term = "token", group = c("doc_id", "paragraph_id", "sentence_id"), relevant = x$upos %in% c("NOUN", "ADJ"), ngram_max = 3, n_min = 5) ## Find simple noun phrases x$phrase_tag <- as_phrasemachine(x$upos, type = "upos") keyw_nounphrases <- keywords_phrases(x$phrase_tag, term = x$token, pattern = "(A|N)*N(P+D*(A|N)*N)*", is_regex = TRUE, detailed = FALSE) keyw_nounphrases <- subset(keyw_nounphrases, ngram > 1) ## Recode terms to keywords x$term <- x$token x$term <- txt_recode_ngram(x$term, compound = keyw_rake$keyword, ngram = keyw_rake$ngram) x$term <- txt_recode_ngram(x$term, compound = keyw_nounphrases$keyword, ngram = keyw_nounphrases$ngram) ## Keep keyword or just plain nouns x$term <- ifelse(x$upos %in% "NOUN", x$term, ifelse(x$term %in% c(keyw_rake$keyword, keyw_nounphrases$keyword), x$term, NA)) ## Build document/term/matrix dtm <- document_term_frequencies(x, document = "topic_level_id", term = "term") dtm <- document_term_matrix(x = dtm) dtm <- dtm_remove_lowfreq(dtm, minfreq = 5)
Once we have our document/term/matrix, topic modelling is simple. Keep in mind that you need to tune your topic model, which is not done below. See the topicmodels and ldatuning R package which show you how to do that.
m <- LDA(dtm, k = 3, method = "Gibbs", control = list(nstart = 5, burnin = 2000, best = TRUE, seed = 1:5))
You'll see that the topic model now includes keywords
topicterminology <- predict(m, type = "terms", min_posterior = 0.10, min_terms = 3) topicterminology
In the above exercise, nouns which were part of a compound multi-word-expression (mwe) were replaced by the multi-word-expression. Sometimes however, you want to keep the noun as well as the multi-word expression in the topic model even if the noun is always part of a multi-word expression. You can do this as follows.
## Recode tokens to keywords, if it is not in the list of tokens, set to NA x$mwe <- txt_recode_ngram(x$token, compound = keyw_rake$keyword, ngram = keyw_rake$ngram) x$mwe <- ifelse(x$mwe %in% keyw_rake$keyword, x$mwe, NA) ## nouns x$term_noun <- ifelse(x$upos %in% "NOUN", x$token, NA) ## Build document/term/matrix dtm <- document_term_frequencies(x, document = "topic_level_id", term = c("term_noun", "mwe")) dtm <- document_term_matrix(x = dtm) dtm <- dtm_remove_lowfreq(dtm, minfreq = 3) m <- LDA(dtm, k = 3, method = "Gibbs", control = list(nstart = 5, burnin = 2000, best = TRUE, seed = 1:5))
The textrank R package allows you to easily summarise text, it integrates well with this udpipe R package. It's especially suited for finding a the most relevant sentences of documents of a certain (LDA) topic. More details on that package, see https://CRAN.R-project.org/package=textrank.
Need support in text mining. Contact BNOSAC: http://www.bnosac.be
invisible(if(file.exists("french-gsd-ud-2.4-190531.udpipe")) file.remove(c("french-gsd-ud-2.4-190531.udpipe")))
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