inst/doc/e_doc_summarization.R

In textmineR: Functions for Text Mining and Topic Modeling

## ----setup, include = FALSE---------------------------------------------------
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

## ----embedding----------------------------------------------------------------
library(textmineR)

# load the data
data(movie_review, package = "text2vec")

# let's take a sample so the demo will run quickly
# note: textmineR is generally quite scaleable, depending on your system
set.seed(123)
s <- sample(1:nrow(movie_review), 200)

movie_review <- movie_review[ s , ]

# let's get those nasty "<br />" symbols out of the way
movie_review$review <- stringr::str_replace_all(movie_review$review, "<br */>", "")

# First create a TCM using skip grams, we'll use a 5-word window
# most options available on CreateDtm are also available for CreateTcm
tcm <- CreateTcm(doc_vec = movie_review$review,
                 skipgram_window = 10,
                 verbose = FALSE,
                 cpus = 2)

# use LDA to get embeddings into probability space
# This will take considerably longer as the TCM matrix has many more rows 
# than a DTM
embeddings <- FitLdaModel(dtm = tcm,
                          k = 50,
                          iterations = 200,
                          burnin = 180,
                          alpha = 0.1,
                          beta = 0.05,
                          optimize_alpha = TRUE,
                          calc_likelihood = FALSE,
                          calc_coherence = FALSE,
                          calc_r2 = FALSE,
                          cpus = 2)


## ----eval = FALSE-------------------------------------------------------------
#    # parse it into sentences
#    sent <- stringi::stri_split_boundaries(doc, type = "sentence")[[ 1 ]]
#  
#    names(sent) <- seq_along(sent) # so we know index and order
#  
#    # embed the sentences in the model
#    e <- CreateDtm(sent, ngram_window = c(1,1), verbose = FALSE, cpus = 2)
#  
#    # remove any documents with 2 or fewer words
#    e <- e[ rowSums(e) > 2 , ]
#  
#    vocab <- intersect(colnames(e), colnames(gamma))
#  
#    e <- e / rowSums(e)
#  
#    e <- e[ , vocab ] %*% t(gamma[ , vocab ])
#  
#    e <- as.matrix(e)
#  

## ----eval = FALSE-------------------------------------------------------------
#    # get the pairwise distances between each embedded sentence
#    e_dist <- CalcHellingerDist(e)

## ----eval = FALSE-------------------------------------------------------------
#    # turn into a similarity matrix
#    g <- (1 - e_dist) * 100

## ----eval = FALSE-------------------------------------------------------------
#    # we don't need sentences connected to themselves
#    diag(g) <- 0
#  
#    # turn into a nearest-neighbor graph
#    g <- apply(g, 1, function(x){
#      x[ x < sort(x, decreasing = TRUE)[ 3 ] ] <- 0
#      x
#    })
#  
#    # by taking pointwise max, we'll make the matrix symmetric again
#    g <- pmax(g, t(g))

## ----eval = FALSE-------------------------------------------------------------
#    g <- graph.adjacency(g, mode = "undirected", weighted = TRUE)
#  
#    # calculate eigenvector centrality
#    ev <- evcent(g)
#  
#    # format the result
#    result <- sent[ names(ev$vector)[ order(ev$vector, decreasing = TRUE)[ 1:3 ] ] ]
#  
#    result <- result[ order(as.numeric(names(result))) ]
#  
#    paste(result, collapse = " ")

## ----summaries----------------------------------------------------------------

library(igraph) 

# let's do this in a function

summarizer <- function(doc, gamma) {
  
  # recursive fanciness to handle multiple docs at once
  if (length(doc) > 1 )
    # use a try statement to catch any weirdness that may arise
    return(sapply(doc, function(d) try(summarizer(d, gamma))))
  
  # parse it into sentences
  sent <- stringi::stri_split_boundaries(doc, type = "sentence")[[ 1 ]]
  
  names(sent) <- seq_along(sent) # so we know index and order
  
  # embed the sentences in the model
  e <- CreateDtm(sent, ngram_window = c(1,1), verbose = FALSE, cpus = 2)
  
  # remove any documents with 2 or fewer words
  e <- e[ rowSums(e) > 2 , ]
  
  vocab <- intersect(colnames(e), colnames(gamma))
  
  e <- e / rowSums(e)
  
  e <- e[ , vocab ] %*% t(gamma[ , vocab ])
  
  e <- as.matrix(e)
  
  # get the pairwise distances between each embedded sentence
  e_dist <- CalcHellingerDist(e)
  
  # turn into a similarity matrix
  g <- (1 - e_dist) * 100
  
  # we don't need sentences connected to themselves
  diag(g) <- 0
  
  # turn into a nearest-neighbor graph
  g <- apply(g, 1, function(x){
    x[ x < sort(x, decreasing = TRUE)[ 3 ] ] <- 0
    x
  })

  # by taking pointwise max, we'll make the matrix symmetric again
  g <- pmax(g, t(g))
  
  g <- graph.adjacency(g, mode = "undirected", weighted = TRUE)
  
  # calculate eigenvector centrality
  ev <- evcent(g)
  
  # format the result
  result <- sent[ names(ev$vector)[ order(ev$vector, decreasing = TRUE)[ 1:3 ] ] ]
  
  result <- result[ order(as.numeric(names(result))) ]
  
  paste(result, collapse = " ")
}

## -----------------------------------------------------------------------------
# Let's see the summary of the first couple of reviews
docs <- movie_review$review[ 1:3 ]
names(docs) <- movie_review$id[ 1:3 ]

sums <- summarizer(docs, gamma = embeddings$gamma)

sums