README.md

In ChengMengli/topic: Functions for Text Mining and Topic Modeling

textmineR

Functions for Text Mining and Topic Modeling

An aid for text mining in R, with a syntax that is more familiar to experienced R users. Also, implements various functions related to topic modeling. It works well with with the "lda" package by J. Chang.

Below is a demo of some of the functionality in textmineR

Example using LDA topic modeling

library(textmineR)

# Load some data into the workspace 
data(nih_sample)

# Create a document term matrix
dtm <- CreateDtm(nih_sample$ABSTRACT_TEXT, 
                 doc_names = nih_sample$APPLICATION_ID, 
                 ngram_window = c(1, 2))

dim(dtm)

# explore basic frequencies & curate vocabulary
tf <- TermDocFreq(dtm = dtm)

# Eliminate words appearing less than 2 times or in more than half of the
# documents
vocabulary <- tf$term[ tf$term_freq > 1 & tf$doc_freq < nrow(dtm) / 2 ]

dtm <- dtm[ , vocabulary]

dim(dtm)

# fit some LDA models and select the best number of topics
k_list <- seq(5, 50, by = 5)

model_dir <- paste0("models_", digest::digest(vocabulary, algo = "sha1"))

if (!dir.exists(model_dir)) dir.create(model_dir)

model_list <- TmParallelApply(X = k_list, FUN = function(k){
  filename = file.path(model_dir, paste0(k, "_topics.rda"))

  if (!file.exists(filename)) {
    m <- FitLdaModel(dtm = dtm, k = k, iterations = 500)
    m$k <- k
    m$coherence <- CalcProbCoherence(phi = m$phi, dtm = dtm, M = 5)
    save(m, file = filename)
  } else {
    load(filename)
  }

  m
}, export=c("dtm", "model_dir")) # export only needed for Windows machines

coherence_mat <- data.frame(k = sapply(model_list, function(x) nrow(x$phi)), 
                            coherence = sapply(model_list, function(x) mean(x$coherence)), 
                            stringsAsFactors = FALSE)

plot(coherence_mat, type = "o")

# select k based on maximum average coherence
model <- model_list[ which.max(coherence_mat$coherence) ][[ 1 ]]


names(model) # phi is P(words | topics), theta is P(topics | documents)

# Calculate some summary statistics etc. Which is the real value-add of textmineR

# Get the R-squared of this model
model$r2 <- CalcTopicModelR2(dtm = dtm, phi = model$phi, theta = model$theta)

model$r2

# top 5 terms of the model according to phi & phi-prime
model$top_terms <- GetTopTerms(phi = model$phi, M = 5)

# phi-prime, P(topic | words) for classifying new documents
model$phi_prime <- CalcPhiPrime(phi = model$phi, theta = model$theta, p_docs = rowSums(dtm))

model$top_terms_prime <- GetTopTerms(phi = model$phi_prime, M = 5)

# give a hard in/out assignment of topics in documents
model$assignments <- model$theta

model$assignments[ model$assignments < 0.05 ] <- 0

model$assignments <- model$assignments / rowSums(model$assignments)

model$assignments[ is.na(model$assignments) ] <- 0


# Get some topic labels using n-grams from the DTM
model$labels <- LabelTopics(assignments = model$assignments, 
                            dtm = dtm,
                            M = 2)

# Probabilistic coherence: measures statistical support for a topic
model$coherence <- CalcProbCoherence(phi = model$phi, dtm = dtm, M = 5)


# Number of documents in which each topic appears
model$num_docs <- colSums(model$assignments > 0)

# cluster topics together in a dendrogram
model$topic_linguistic_dist <- CalcHellingerDist(model$phi)

model$hclust <- hclust(as.dist(model$topic_linguistic_dist), "ward.D")

model$hclust$clustering <- cutree(model$hclust, k = 10)

model$hclust$labels <- paste(model$hclust$labels, model$labels[ , 1])

plot(model$hclust)
rect.hclust(model$hclust, k = length(unique(model$hclust$clustering)))

# make a summary table
model$summary <- data.frame(topic     = rownames(model$phi),
                            cluster   = model$hclust$clustering,
                            model$labels,
                            coherence = model$coherence,
                            num_docs  = model$num_docs,
                            top_terms = apply(model$top_terms, 2, function(x){
                              paste(x, collapse = ", ")
                            }),
                            top_terms_prime = apply(model$top_terms_prime, 2, function(x){
                              paste(x, collapse = ", ")
                            }),
                            stringsAsFactors = FALSE)

View(model$summary[ order(model$hclust$clustering) , ])

Example of document summarization

rm(list=ls())

library(textmineR)

data(nih_sample)


# Select a document

doc <- nih_sample$ABSTRACT_TEXT[ 10 ]

# Parse it into sentences
doc <- stringi::stri_split_boundaries(doc, type = "sentence")[[ 1 ]]

names(doc) <- seq(along = doc)

# Turn those sentences into a DTM, use stemming & bi-grams
dtm <- CreateDtm(doc, 
                 ngram_window = c(1, 2),
                 stem_lemma_function = function(x) SnowballC::wordStem(x, "porter"))

# TF-IDF Frequency re-weighting
idf <- log(nrow(dtm) / colSums(dtm > 0))

tfidf <- t(dtm) * idf

tfidf <- t(tfidf)

# Calculate document-to-document cosine similarity
csim <- tfidf / sqrt(rowSums(tfidf * tfidf))

csim <- csim %*% t(csim)

# Turn that cosine similarity matrix into a nearest-neighbor network
nn <- csim

diag(nn) <- 0

nn <- apply(nn, 1, function(x){
  x[ x < sort(x, decreasing = TRUE)[ 2 ] ] <- 0
  x
})

nn <- nn * 100

g <- igraph::graph_from_adjacency_matrix(nn, mode = "directed", weighted = TRUE)

plot(g)

# Calculate eigenvalue centrality
ec <- igraph::eigen_centrality(g)

# Return top 3 central sentences as the summary
summary <- doc[ names(ec[[ 1 ]])[ order(ec[[ 1 ]], decreasing = T) ][ 1:2 ] ]

summary <- summary[ order(as.numeric(names(summary))) ]

paste(summary, collapse = " ")

ChengMengli/topic documentation built on May 31, 2019, 8:44 p.m.