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Sentiment Analysis

Sentiment

Definition:

The process of computationally identifying and categorizing opinions expressed in a piece of text, especially in order to determine whether the writer’s attitude towards a particular topic, product, etc. is positive, negative, or neutral

Use case:

Customer’s on line comments/feedback from an insurance companies website has been scrapped to run through the sentiment analysis.

You can find full R code along with the data set in my git repository here

Steps:

  • Load required R libraries

    # source("http://bioconductor.org/biocLite.R")
# biocLite("Rgraphviz")
# install.packages('tm')
# install.packages('wordcloud')
# download.file("http://cran.cnr.berkeley.edu/src/contrib/Archive/Rstem/Rstem_0.4-1.tar.gz", "Rstem_0.4-1.tar.gz")
# install.packages("Rstem_0.4-1.tar.gz", repos=NULL, type="source")
# download.file("http://cran.r-project.org/src/contrib/Archive/sentiment/sentiment_0.2.tar.gz", "sentiment.tar.gz")
# install.packages("sentiment.tar.gz", repos=NULL, type="source")# Load libraries

library(wordcloud)
library(tm)
library(plyr)
library(ggplot2)
library(grid)
library(sentiment)
library(Rgraphviz)

  • Pre-process data:

    Text pre-processing is an important step to reduce noise from the data. Each step is discussed below

  • convert to lower: this is to avoid distinguish between words simply on case
  • remove punctuation: punctuation can provide grammatical context which supports understanding. Often for initial analyses we ignore the punctuation
  • remove numbers: numbers may or may not be relevant to our analyses
  • remove stop words: stop words are common words found in a language. Words like for, of, are etc are common stop word
  • create document term matrix: a document term matrix is simply a matrix with documents as the rows and terms as the columns and a count of the frequency of words as the cells of the matrix
df <- read.table("../input/data.csv",sep=",",header=TRUE)
corp <- Corpus(VectorSource(df$Review)) 
corp <- tm_map(corp, tolower) 
corp <- tm_map(corp, removePunctuation)
corp <- tm_map(corp, removeNumbers)
# corp <- tm_map(corp, stemDocument, language = "english") 
corp <- tm_map(corp, removeWords, c("the", stopwords("english"))) 
corp <- tm_map(corp, PlainTextDocument)
corp.tdm <- TermDocumentMatrix(corp, control = list(minWordLength = 3)) 
corp.dtm <- DocumentTermMatrix(corp, control = list(minWordLength = 3))

  • Insight through visualization

    • Word cloud: This visualization generates words whose font size relates to its frequency.

      wordcloud(corp, scale=c(5,0.5), max.words=100, random.order=FALSE, rot.per=0.35, use.r.layout=FALSE, colors=brewer.pal(8, 'Dark2'))

      Word Cloud

    • Frequency plot:This visualization presents a bar chart whose length corresponds the frequency a particular word occurred 
      corp.tdm.df <- sort(rowSums(corp.tdm.df),decreasing=TRUE) # populate term frequency and sort in decesending order
df.freq <- data.frame(word = names(corp.tdm.df),freq=corp.tdm.df) # Table with terms and frequency

# Set minimum term frequency value. The charts will be created for terms > or = to the minimum value that we set.
freqControl <- 100
      # Frequency Plot
freqplotData <- subset(df.freq, df.freq$freq > freqControl)
freqplotData$word <- ordered(freqplotData$word,levels=levels(freqplotData$word)[unclass(freqplotData$word)])
freqplot <- ggplot(freqplotData,aes(reorder(word,freq), freq))
freqplot <- freqplot + geom_bar(stat="identity")
freqplot <- freqplot + theme(axis.text.x=element_text(angle=90,hjust=1)) + coord_flip() 
freqplot + xlim(rev(levels(freqplotData$word)))+ ggtitle("Frequency Plot")

      Frequency.png

    • Correlation plot: Here, we choose N number of high frequent words as the nodes and include links between words when they have at least a correlation of x % 
      # Correlation Plot
# 50 of the more frequent words have been chosen as the nodes and include links between words
# when they have at least a correlation of 0.2
# By default (without providing terms and a correlation threshold) the plot function chooses a
# random 20 terms with a threshold of 0.7
plot(corp.tdm,terms=findFreqTerms(corp.tdm,lowfreq=freqControl)[1:50],corThreshold=0.2, main="Correlation Plot")

      Correlation.png

    • Paired word cloud: This is a customized word cloud. Here, we pick the top N most frequent words and extract associated words with strong correlation. Combine individual top N words with the every associated word (say one of my top words is broken and one of the associated words is pipe; the combined word would be broken-pipe). Then we create a word cloud on the combined words. Although the concept is good, the chart below does not appear helpful. So need to figure out a better representation

      # Paired-Terms wordcloud
# pick the top N most frequent words and extract associated words with strong correlation (say 70%). 
# Combine individual top N words with every associated word.
nFreqTerms <- findFreqTerms(corp.dtm,lowfreq=freqControl)
nFreqTermsAssocs <- findAssocs(corp.dtm, nFreqTerms, 0.3)
pairedTerms <- c()
for (i in 1:length(nFreqTermsAssocs)){
  if(length(names(nFreqTermsAssocs[[i]]))!=0) 
    lapply(names(nFreqTermsAssocs[[i]]),function(x) pairedTerms <<- c(pairedTerms,paste(names(nFreqTermsAssocs[i]),x,sep="-")))
}
wordcloud(pairedTerms,random.order=FALSE,colors=dark2,main="Paired Wordcloud")

      Paired Word Cloud

  • Sentiment Score

    • Load positive / negative terms corpus

      The corpus contains around 6800 words, this list was compiled over many years starting from first paper by Hu and Liu, KDD-2004. Although necessary, having an opinion lexicon is far from sufficient for accurate sentiment analysis. See this paper: Sentiment Analysis and Subjectivity or the Sentiment Analysis

    • Calculate positive / negative score

      Simply we calculate the positive / negative score by comparing the terms with positive/negative term corpus and summing the occurrence count

    • Classify emotion

      R package sentiment by Timothy Jurka has a function that helps us to analyze some text and classify it in different types of emotion: anger, disgust, fear, joy, sadness, and surprise. The classification can be performed using two algorithms: one is a naive Bayes classifier trained on Carlo Strapparava and Alessandro Valitutti’s emotions lexicon; the other one is just a simple voter procedure.

    • Classify polarity

      Another function from sentiment package, classify_polarity allows us to classify some text as positive or negative. In this case, the classification can be done by using a naive Bayes algorithm trained on Janyce Wiebe’s subjectivity lexicon; or by a simple voter algorithm.

      hu.liu.pos = scan('../input/positive-words.txt', what = 'character',comment.char=';') 
hu.liu.neg = scan('../input/negative-words.txt',what = 'character',comment.char= ';') 
pos.words = c(hu.liu.pos)
neg.words = c(hu.liu.neg)
score.sentiment = function(sentences, pos.words, neg.words, .progress='none')
{
  require(plyr)
  require(stringr)
  
  # we got a vector of sentences. plyr will handle a list
  # or a vector as an "l" for us
  # we want a simple array ("a") of scores back, so we use
  # "l" + "a" + "ply" = "laply":
  scores = laply(sentences, function(sentence, pos.words, neg.words) {
    
    # clean up sentences with R's regex-driven global substitute, gsub():
    sentence = gsub('[[:punct:]]', '', sentence)
    sentence = gsub('[[:cntrl:]]', '', sentence)
    sentence = gsub('\\d+', '', sentence)
    # and convert to lower case:
    sentence = tolower(sentence)
    
    # split into words. str_split is in the stringr package
    word.list = str_split(sentence, '\\s+')
    # sometimes a list() is one level of hierarchy too much
    words = unlist(word.list)
    
    # compare our words to the dictionaries of positive & negative terms
    pos.matches = match(words, pos.words)
    neg.matches = match(words, neg.words)
    
    # match() returns the position of the matched term or NA
    # we just want a TRUE/FALSE:
    pos.matches= !is.na(pos.matches)
    neg.matches= !is.na(neg.matches)
    
    # and conveniently enough, TRUE/FALSE will be treated as 1/0 by sum():
    score = sum(pos.matches) - sum(neg.matches)
    
    return(score)
  }, pos.words, neg.words, .progress=.progress )
  
  scores.df = data.frame(score=scores, text=sentences)
  return(scores.df)
}

review.scores<- score.sentiment(df$Review,pos.words,neg.words,.progress='text')
      #classify emotion
class_emo = classify_emotion(df$Review, algorithm="bayes", prior=1.0)
#get emotion best fit
emotion = class_emo[,7]
# substitute NA's by "unknown"
emotion[is.na(emotion)] = "unknown"

# classify polarity
class_pol = classify_polarity(df$Review, algorithm="bayes")

# get polarity best fit
polarity = class_pol[,4]

# data frame with results
sent_df = data.frame(text=df$Review, emotion=emotion, polarity=polarity, stringsAsFactors=FALSE)

# sort data frame
sent_df = within(sent_df, emotion <- factor(emotion, levels=names(sort(table(emotion), decreasing=TRUE))))

    • Visualize

      • Distribution of overall score
        ggplot(review.scores, aes(x=score)) + 
  geom_histogram(binwidth=1) + 
  xlab("Sentiment score") + 
  ylab("Frequency") + 
  ggtitle("Distribution of sentiment score") +
  theme_bw()  + 
  theme(axis.title.x = element_text(vjust = -0.5, size = 14)) + 
  theme(axis.title.y=element_text(size = 14, angle=90, vjust = -0.25)) + 
  theme(plot.margin = unit(c(1,1,2,2), "lines"))

        Sentiment Score Distribution.png

      • Distribution of score for a given term
        review.pos<- subset(review.scores,review.scores$score>= 2) 
review.neg<- subset(review.scores,review.scores$score<= -2)
claim <- subset(review.scores, regexpr("claim", review.scores$text) > 0) 
ggplot(claim, aes(x = score)) + geom_histogram(binwidth = 1) + ggtitle("Sentiment score for the token 'claim'") + xlab("Score") + ylab("Frequency") + theme_bw()  + theme(axis.title.x = element_text(vjust = -0.5, size = 14)) + theme(axis.title.y = element_text(size = 14, angle = 90, vjust = -0.25)) + theme(plot.margin = unit(c(1,1,2,2), "lines"))

        Claim Score.png

      • Distribution of emotion
        # plot distribution of emotions
ggplot(sent_df, aes(x=emotion)) +
  geom_bar(aes(y=..count.., fill=emotion)) +
  scale_fill_brewer(palette="Dark2") +
  labs(x="emotion categories", y="number of Feedback", 
       title = "Sentiment Analysis of Feedback about claim(classification by emotion)",
       plot.title = element_text(size=12))

        Emotions Distribution.png

      • Distribution of polarity
        # plot distribution of polarity
ggplot(sent_df, aes(x=polarity)) +
  geom_bar(aes(y=..count.., fill=polarity)) +
  scale_fill_brewer(palette="RdGy") +
  labs(x="emotion categories", y="number of Feedback", 
       title = "Sentiment Analysis of Feedback about claim(classification by emotion)",
       plot.title = element_text(size=12))

        Polarity.png

      • Text by emotion
        # separating text by emotion
emos = levels(factor(sent_df$emotion))
nemo = length(emos)
emo.docs = rep("", nemo)
for (i in 1:nemo)
{
  tmp = df$Review[emotion == emos[i]]
  emo.docs[i] = paste(tmp, collapse=" ")
}

# remove stopwords
emo.docs = removeWords(emo.docs, stopwords("english"))
# create corpus
corpus = Corpus(VectorSource(emo.docs))
tdm = TermDocumentMatrix(corpus)
tdm = as.matrix(tdm)
colnames(tdm) = emos

# comparison word cloud
comparison.cloud(tdm, colors = brewer.pal(nemo, "Dark2"),
                 scale = c(3,.5), random.order = FALSE, title.size = 1.5)

        Text by emotion.png

Next post to cover sentiment analysis in R + Hadoop.

 

Reference:

The above write up is based on the tutorials from following links: