Social Media

Did you know that Twitter, the online news and social networking service provider, has 320 million users, with an average of 42 million active tweets every day! (Source: Global social media research summary 2016 by smartinsights).

Let’s understand how to explore the rich information of social media (I’ll consider Twitter as an example) to explore what is being spoken about a chosen topic. Most of these forums provide API for developers to access the posts. See Figure 5-2.

Figure 5-2. Pulling Twitter posts for analysis

Step 1 – Get Access Key (One-Time Activity)

Follow the below steps to set up a new Twitter app to get consumer/access key, secret, and token (do not share the key token with unauthorized persons).

• Go to https://apps.twitter.com/

• Click on ‘Create New App’

• Fill the required information and click on ‘Create your Twitter Application’

• You’ll get the access details under ‘Keys and Access Tokens’ tab

Step 2 – Fetching Tweets

Once you have the authorization secret and access tokens, you can use the below code in Listing 5-2 to establish the connection.

Listing 5-2. Twitter authentication

#Import the necessary methods from tweepy library
import tweepy
from tweepy.streaming import StreamListener
from tweepy import OAuthHandler
from tweepy import Stream

#provide your access details below
access_token = "Your token goes here"
access_token_secret = "Your token secret goes here"
consumer_key = "Your consumer key goes here"
consumer_secret = "Your consumer secret goes here"

# establish a connection
auth = tweepy.auth.OAuthHandler(consumer_key, consumer_secret)
auth.set_access_token(access_token, access_token_secret)

api = tweepy.API(auth)

Let’s assume that you would like to understand what is being said about the iPhone 7 and its camera feature. So let’s pull the most recent 10 posts.

#fetch recent 10 tweets containing words iphone7, camera
fetched_tweets = api.search(q=['iPhone 7','iPhone7','camera'], result_type='recent', lang='en', count=10)
print “Number of tweets: ”,len(fetched_tweets)
#----output----
Number of tweets:  10

# Print the tweet text
for tweet in fetched_tweets:
    print 'Tweet ID: ', tweet.id
    print 'Tweet Text: ', tweet.text, '\n'
#----output----
Tweet ID:  825155021390049281
Tweet Text:  RT @volcanojulie: A Tau Emerald dragonfly. The iPhone 7 camera is exceptional!
#nature #insect #dragonfly #melbourne #australia #iphone7 #...

Tweet ID:  825086303318507520
Tweet Text:  Fuzzy photos? Protect your camera lens instantly with #iPhone7 Full Metallic Case. Buy now! https://t.co/d0dX40BHL6 https://t.co/AInlBoreht

You can capture useful features onto a dataframe for further analysis. See Listing 5-3.

Listing 5-3. Save features to dataframe

# function to save required basic tweets info to a dataframe
def populate_tweet_df(tweets):
    #Create an empty dataframe
    df = pd.DataFrame()

    df['id'] = list(map(lambda tweet: tweet.id, tweets))
    df['text'] = list(map(lambda tweet: tweet.text, tweets))
    df['retweeted'] = list(map(lambda tweet: tweet.retweeted, tweets))
    df['place'] = list(map(lambda tweet: tweet.user.location, tweets))
    df['screen_name'] = list(map(lambda tweet: tweet.user.screen_name, tweets))
    df['verified_user'] = list(map(lambda tweet: tweet.user.verified, tweets))
    df['followers_count'] = list(map(lambda tweet: tweet.user.followers_count, tweets))
    df['friends_count'] = list(map(lambda tweet: tweet.user.friends_count, tweets))

    # Highly popular user's tweet could possibly seen by large audience, so lets check the popularity of user
    df['friendship_coeff'] = list(map(lambda tweet: float(tweet.user.followers_count)/float(tweet.user.friends_count), tweets))
    return df

df = populate_tweet_df(fetched_tweets)
print df.head(10)
#---output----
                   id                                               text
0  825155021390049281  RT @volcanojulie: A Tau Emerald dragonfly. The...
1  825086303318507520  Fuzzy photos? Protect your camera lens instant...
2  825064476714098690  RT @volcanojulie: A Tau Emerald dragonfly. The...
3  825062644986023936  RT @volcanojulie: A Tau Emerald dragonfly. The...
4  824935025217040385  RT @volcanojulie: A Tau Emerald dragonfly. The...
5  824933631365779458  A Tau Emerald dragonfly. The iPhone 7 camera i...
6  824836880491483136  The camera on the IPhone 7 plus is fucking awe...
7  823805101999390720  'Romeo and Juliet' Ad Showcases Apple's iPhone...
8  823804251117850624  iPhone 7 Images Show Bigger Camera Lens - I ha...
9  823689306376196096  RT @computerworks5: Premium HD Selfie Stick &a...

  retweeted                          place      screen_name verified_user
0     False            Melbourne, Victoria        MonashEAE         False
1     False                California, USA        ShopNCURV         False
2     False    West Islip, Long Island, NY  FusionWestIslip         False
3     False  6676 Fresh Pond Rd Queens, NY  FusionRidgewood         False
4     False                                   Iphone7review         False
5     False   Melbourne; Monash University     volcanojulie         False
6     False                  Hollywood, FL       Hbk_Mannyp         False
7     False       Toronto.NYC.the Universe  AaronRFernandes         False
8     False                 Lagos, Nigeria    moyinoluwa_mm         False
9     False                                   Iphone7review         False

   followers_count  friends_count  friendship_coeff
0              322            388          0.829897
1              279            318          0.877358
2               13            193          0.067358
3               45            218          0.206422
4              199           1787          0.111360
5              398            551          0.722323
6               57             64          0.890625
7            18291              7       2613.000000
8              780            302          2.582781
9              199           1787          0.111360

Instead of a topic you can also choose a screen_name focused on a topic; let’s look at the posts by the screen name Iphone7review. See Listing 5-4.

Listing 5-4. Example code for extracting tweets based on screen name

# For help about api look here http://tweepy.readthedocs.org/en/v2.3.0/api.html
fetched_tweets =  api.user_timeline(id='Iphone7review', count=5)

# Print the tweet text
for tweet in fetched_tweets:
    print 'Tweet ID: ', tweet.id
    print 'Tweet Text: ', tweet.text, '\n'
#----output----
Tweet ID:  825169063676608512
Tweet Text:  RT @alicesttu: iPhone 7S to get Samsung OLED display next year #iPhone https://t.co/BylKbvXgAG #iphone

Tweet ID:  825169047138533376
Tweet Text:  Nothing beats the Iphone7! Who agrees? #Iphone7 https://t.co/e03tXeLOao

Glancing through the posts quickly can generally help you conclude that there are positive comments about the camera feature of iPhone 7.

Convert to Lower Case and Tokenize

Here, all the data is converted into lowercase. This is carried out to prevent words like “LIKE” or “Like” being interpreted as different words. Python provides a function lower() to convert text to lowercase.

Tokenizing is the process of breaking a large set of texts into smaller meaningful chunks such as sentences, words, and phrases.

import nltk
from nltk.tokenize import sent_tokenize

text='Statistics skills, and programming skills are equally important for analytics. Statistics skills, and domain knowledge are important for analytics. I like reading books and travelling.'

sent_tokenize_list = sent_tokenize(text)
print(sent_tokenize_list)
#----output----
['Statistics skills, and programming skills are equally important for analytics.', 'Statistics skills, and domain knowledge are important for analytics.', 'I like reading books and travelling.']

import nltk.data
spanish_tokenizer = nltk.data.load('tokenizers/punkt/spanish.pickle')
spanish_tokenizer.tokenize('Hola. Esta es una frase espanola.')
#----output----
['Hola.', 'Esta es una frase espanola.']

from nltk.tokenize import word_tokenize
print word_tokenize(text)

# Another equivalent call method using TreebankWordTokenizer
from nltk.tokenize import TreebankWordTokenizer
tokenizer = TreebankWordTokenizer()
print tokenizer.tokenize(text)
#----output----

Removing Noise

You should remove all information that is not comparative or relevant to text analytics. These can be seen as noise to the text analytics. Most common noises are numbers, punctuations, stop words, white space, etc

Numbers: Numbers are removed as they may not be relevant and not hold valuable information. See Listing 5-8.

Listing 5-8. Example code for removing noise from text

def remove_numbers(text):
    return re.sub(r'\d+', '', text)

text = 'This is a    sample  English  sentence, \n with whitespace and numbers 1234!'
print 'Removed numbers: ', remove_numbers(text)
#----output----
Removed numbers:  This is a     sample  English   sentence,
 with whitespace and numbers !

Punctuation: It is to be removed for better identifying each word and remove punctuation characters from the dataset. For example “like” and “like” or “coca-cola” and “cocacola” would be interpreted as different words if the punctuation was not removed. See Listing 5-9.

Listing 5-9. Example code for removing punctuation from text

import string

# Function to remove punctuations
def remove_punctuations(text):
    words = nltk.word_tokenize(text)
    punt_removed = [w for w in words if w.lower() not in string.punctuation]
    return " ".join(punt_removed)

print remove_punctuations('This is a sample English sentence, with punctuations!')
#----output----
This is a sample English sentence with punctuations

Stop words: Words like “the,” “and,” “or” are uninformative and add unneeded noise to the analysis. For this reason they are removed. See Listing 5-10.

Listing 5-10. Example code for removing stop words from text

from nltk.corpus import stopwords

# Function to remove stop words
def remove_stopwords(text, lang='english'):
    words = nltk.word_tokenize(text)
    lang_stopwords = stopwords.words(lang)
    stopwords_removed = [w for w in words if w.lower() not in lang_stopwords]
    return " ".join(stopwords_removed)

print remove_stopwords('This is a sample English sentence')
#----output----
sample English sentence

Whitespace: Often in text analytics, an extra whitespace (space, tab, Carriage Return, Line Feed) becomes identified as a word. This anomaly is avoided through a basic programming procedure in this step. See Listing 5-11.

Listing 5-11. Example code for removing whitespace from text

# Function to remove whitespace
def remove_whitespace(text):
    return " ".join(text.split())
text = 'This is a     sample  English   sentence, \n with whitespace and numbers 1234!'
print 'Removed whitespace: ', remove_whitespace(text)
#----output----
Removed whitespace:  This is a sample English sentence, with whitespace and numbers 1234!

Part of Speech (PoS) Tagging

PoS tagging is the process of assigning language-specific parts of speech such as nouns, verbs, adjectives, and adverbs, etc., for each word in the given text.

NLTK supports multiple PoS tagging models, and the default tagger is maxent_treebank_pos_tagger, which uses Penn (Pennsylvania University) Tree bank corpus. The same has 36 possible parts of speech tags, a sentence (S) is represented by the parser as a tree having three children: a noun phrase (NP), a verbal phrase (VP), and the full stop (.). The root of the tree will be S. See Table 5-3 and Listings 5-12 and 5-13.

Listing 5-12. Example code for PoS, the sentence, and visualize sentence tree

from nltk import chunk

tagged_sent = nltk.pos_tag(nltk.word_tokenize('This is a sample English sentence'))
print tagged_sent

tree = chunk.ne_chunk(tagged_sent)
tree.draw() # this will draw the sentence tree
#----output----
[('This', 'DT'), ('is', 'VBZ'), ('a', 'DT'), ('sample', 'JJ'), ('English', 'JJ'), ('sentence', 'NN')]

Listing 5-13. Example code for using perceptron tagger and getting help on tags

# To use PerceptronTagger
from nltk.tag.perceptron import PerceptronTagger
PT = PerceptronTagger()
print PT.tag('This is a sample English sentence'.split())
#----output----
[('This', 'DT'), ('is', 'VBZ'), ('a', 'DT'), ('sample', 'JJ'), ('English', 'JJ'), ('sentence', 'NN')]

# To get help about tags
nltk.help.upenn_tagset('NNP')
#----output----
NNP: noun, proper, singular

Stemming

It is the process of transforming to the root word, that is, it uses an algorithm that removes common word endings from English words, such as “ly,” “es,” “ed,” and “s.” For example, assuming for an analysis you may want to consider “carefully,” “cared,” “cares,” “caringly” as “care” instead of separate words. There are three widely used stemming algorithms as listed in Figure 5-3. See Listing 5-14.

Figure 5-3. Most popular NLTK stemmers

Listing 5-14. Example code for stemming

from nltk import PorterStemmer, LancasterStemmer, SnowballStemmer

# Function to apply stemming to a list of words
def words_stemmer(words, type="PorterStemmer", lang="english", encoding="utf8"):
    supported_stemmers = ["PorterStemmer","LancasterStemmer","SnowballStemmer"]
    if type is False or type not in supported_stemmers:
        return words
    else:
        stem_words = []
        if type == "PorterStemmer":
            stemmer = PorterStemmer()
            for word in words:
                stem_words.append(stemmer.stem(word).encode(encoding))
        if type == "LancasterStemmer":
            stemmer = LancasterStemmer()
            for word in words:
                stem_words.append(stemmer.stem(word).encode(encoding))
        if type == "SnowballStemmer":
            stemmer = SnowballStemmer(lang)
            for word in words:
                stem_words.append(stemmer.stem(word).encode(encoding))
        return " ".join(stem_words)

words =  'caring cares cared caringly carefully'

print "Original: ", words
print "Porter: ", words_stemmer(nltk.word_tokenize(words), "PorterStemmer")
print "Lancaster: ", words_stemmer(nltk.word_tokenize(words), "LancasterStemmer")
print "Snowball: ", words_stemmer(nltk.word_tokenize(words), "SnowballStemmer")
#----output----
Original:  caring cares cared caringly carefully
Porter:  care care care caringli care
Lancaster:  car car car car car
Snowball:  care care care care care

Lemmatization

It is the process of transforming to the dictionary base form. For this you can use WordNet, which is a large lexical database for English words that are linked together by their semantic relationships. It works as a thesaurus, that is, it groups words together based on their meanings. See Listing 5-15.

Listing 5-15. Example code for lemmatization

from nltk.stem import WordNetLemmatizer

wordnet_lemmatizer = WordNetLemmatizer()

# Function to apply lemmatization to a list of words
def words_lemmatizer(text, encoding="utf8"):
    words = nltk.word_tokenize(text)
    lemma_words = []
    wl = WordNetLemmatizer()
    for word in words:
        pos = find_pos(word)
        lemma_words.append(wl.lemmatize(word, pos).encode(encoding))
    return " ".join(lemma_words)

# Function to find part of speech tag for a word
def find_pos(word):
    # Part of Speech constants
    # ADJ, ADJ_SAT, ADV, NOUN, VERB = 'a', 's', 'r', 'n', 'v'
    # You can learn more about these at http://wordnet.princeton.edu/wordnet/man/wndb.5WN.html#sect3
    # You can learn more about all the penn tree tags at https://www.ling.upenn.edu/courses/Fall_2003/ling001/penn_treebank_pos.html
    pos = nltk.pos_tag(nltk.word_tokenize(word))[0][1]
    # Adjective tags - 'JJ', 'JJR', 'JJS'
    if pos.lower()[0] == 'j':
        return 'a'
    # Adverb tags - 'RB', 'RBR', 'RBS'
    elif pos.lower()[0] == 'r':
        return 'r'
    # Verb tags - 'VB', 'VBD', 'VBG', 'VBN', 'VBP', 'VBZ'
    elif pos.lower()[0] == 'v':
        return 'v'
    # Noun tags - 'NN', 'NNS', 'NNP', 'NNPS'
    else:
        return 'n'

print "Lemmatized: ", words_lemmatizer(words)
#----output----
Lemmatized:  care care care caringly carefully

In the above case,‘caringly’/’carefully’ are inflected form of care and they are an entry word listed in WordNet Dictoinary so they are retained in their actual form itself.

NLTK English WordNet includes approximately 155,287 words and 117000 synonym sets. For a given word, WordNet includes/provides definition, example, synonyms (group of nouns, adjectives, verbs that are similar), atonyms (opposite in meaning to another), etc. See Listing 5-16.

Listing 5-16. Example code for wordnet

from nltk.corpus import wordnet

syns = wordnet.synsets("good")
print "Definition: ", syns[0].definition()
print "Example: ", syns[0].examples()

synonyms = []
antonyms = []

# Print  synonums and antonyms (having opposite meaning words)
for syn in wordnet.synsets("good"):
    for l in syn.lemmas():
        synonyms.append(l.name())
        if l.antonyms():
            antonyms.append(l.antonyms()[0].name())

print "synonyms: \n", set(synonyms)
print "antonyms: \n", set(antonyms)
#----output----
Definition:  benefit
Example:  [u'for your own good', u"what's the good of worrying?"]
synonyms:
set([u'beneficial', u'right', u'secure', u'just', u'unspoilt', u'respectable', u'good', u'goodness', u'dear', u'salutary', u'ripe', u'expert', u'skillful', u'in_force', u'proficient', u'unspoiled', u'dependable', u'soundly', u'honorable', u'full', u'undecomposed', u'safe', u'adept', u'upright', u'trade_good', u'sound', u'in_effect', u'practiced', u'effective', u'commodity', u'estimable', u'well', u'honest', u'near', u'skilful', u'thoroughly', u'serious'])
antonyms:
set([u'bad', u'badness', u'ill', u'evil', u'evilness'])

N-grams

One of the important concepts in text mining is n-grams, which are fundamentally a set of co-occurring or continuous sequence of n items from a given sequence of large text. The item here could be words, letters, and syllables. Let’s consider a sample sentence and try to extract n-grams for different values of n. See Listing 5-17.

Listing 5-17. Example code for extracting n-grams from sentence

from nltk.util import ngrams
from collections import Counter

# Function to extract n-grams from text
def get_ngrams(text, n):
    n_grams = ngrams(nltk.word_tokenize(text), n)
    return [ ' '.join(grams) for grams in n_grams]

text = 'This is a sample English sentence'
print "1-gram: ", get_ngrams(text, 1)
print "2-gram: ", get_ngrams(text, 2)
print "3-gram: ", get_ngrams(text, 3)
print "4-gram: ", get_ngrams(text, 4)
#----output----
1-gram:['This', 'is', 'a', 'sample', 'English', 'sentence']
2-gram:['This is', 'is a', 'a sample', 'sample English', 'English sentence']
3-gram:['This is a', 'is a sample', 'a sample English', 'sample English sentence']
4-gram: ['This is a sample', 'is a sample English', 'a sample English sentence']

The N-gram technique is relatively simple and simply increasing the value of n will give us more contexts. It is widely used in the probabilistic language model of predicting the next item in a sequence: for example, search engines use this technique to predict/recommend the possibility of next character/words in the sequence to users as they type. See Listing 5-18.

Listing 5-18. Example code for extracting 2-grams from sentence and store it in a dataframe

text = 'Statistics skills, and programming skills are equally important for analytics. Statistics skills, and domain knowledge are important for analytics'

# remove punctuations
text = remove_punctuations(text)

# Extracting bigrams
result = get_ngrams(text,2)

# Counting bigrams
result_count = Counter(result)

# Converting to the result to a data frame
import pandas as pd
df = pd.DataFrame.from_dict(result_count, orient='index')
df = df.rename(columns={'index':'words', 0:'frequency'}) # Renaming index and column name
print df
#----output----
                      frequency
are equally                   1
domain knowledge              1
skills are                    1
knowledge are                 1
programming skills            1
are important                 1
skills and                    2
for analytics                 2
and domain                    1
important for                 2
and programming               1
Statistics skills             2
equally important             1
analytics Statistics          1

Bag of Words (BoW)

The texts have to be represented as numbers to be able to apply any algorithms. Bag of words is the method where you count the occurrence of words in a document without giving importance to the grammar and the order of words. This can be achieved by creating Term Document Matrix (TDM) . It is simply a matrix with terms as the rows and document names as the columns and a count of the frequency of words as the cells of the matrix. Let’s learn about creating DTM through an example; consider three text documents with some text in it. Sklearn provides good functions under feature_extraction.text to convert a collection of text documents to a matrix of word counts. See Listing 5-19 and Figure 5-4.

Figure 5-4. Document Term Matrix

Listing 5-19. Creating document term matrix from corpus of sample documents

import os
import pandas as pd
from sklearn.feature_extraction.text import CountVectorizer

# Function to create a dictionary with key as file names and values as text for all files in a given folder
def CorpusFromDir(dir_path):
    result = dict(docs = [open(os.path.join(dir_path,f)).read() for f in os.listdir(dir_path)],
               ColNames = map(lambda x: x, os.listdir(dir_path)))
    return result

docs = CorpusFromDir('Data/')

# Initialize
vectorizer = CountVectorizer()
doc_vec = vectorizer.fit_transform(docs.get('docs'))

#create dataFrame
df = pd.DataFrame(doc_vec.toarray().transpose(), index = vectorizer.get_feature_names())

# Change column headers to be file names
df.columns = docs.get('ColNames')
print df
#----output----
             Doc_1.txt  Doc_2.txt  Doc_3.txt
analytics            1          1          0
and                  1          1          1
are                  1          1          0
books                0          0          1
domain               0          1          0
equally              1          0          0
for                  1          1          0
important            1          1          0
knowledge            0          1          0
like                 0          0          1
programming          1          0          0
reading              0          0          1
skills               2          1          0
statistics           1          1          0
travelling           0          0          1

Term Frequency-Inverse Document Frequency (TF-IDF)

In the area of information retrieval, TF-IDF is a good statistical measure to reflect the relevance of the term to the document in a collection of documents or corpus. Let’s break TF_IDF and apply an example to understand it better. See Listing 5-20.

Term frequency will tell you how frequently a given term appears.

For example, consider a document containing 100 words wherein the word ‘ML’ appears 3 times, then TF (ML) = 3 / 100 =0.03

Document frequency will tell you how important a term is?

Assume we have 10 million documents and the word ML appears in one thousand of these, then DF (ML) = 1000/10,000,000 = 0.0001

To normalize let’s take a log (d/D), that is, log (0.0001) = -4

Quite often D > d and log (d/D) will give a negative value as seen in the above example. So to solve this problem let’s invert the ratio inside the log expression, which is known as Inverse document frequency (IDF). Essentially we are compressing the scale of values so that very large or very small quantities are smoothly compared.

Continuing with the above example, IDF(ML) = log(10,000,000 / 1,000) = 4

TF-IDF is the weight product of quantities, that is, for the above example TF-IDF (ML) = 0.03 * 4 = 0.12

sklearn provides provides a function TfidfVectorizer to calculate TF-IDF for text, however by default it normalizes the term vector using L2 normalization and also IDF is smoothed by adding one to the document frequency to prevent zero divisions.

Listing 5-20. Create document term matrix with TF-IDF

from sklearn.feature_extraction.text import TfidfVectorizer

vectorizer = TfidfVectorizer()
doc_vec = vectorizer.fit_transform(docs.get('docs'))
#create dataFrame
df = pd.DataFrame(doc_vec.toarray().transpose(), index = vectorizer.get_feature_names())

# Change column headers to be file names
df.columns = docs.get('ColNames')
print df
#----output----
             Doc_1.txt  Doc_2.txt  Doc_3.txt
analytics     0.276703   0.315269   0.000000
and           0.214884   0.244835   0.283217
are           0.276703   0.315269   0.000000
books         0.000000   0.000000   0.479528
domain        0.000000   0.414541   0.000000
equally       0.363831   0.000000   0.000000
for           0.276703   0.315269   0.000000
important     0.276703   0.315269   0.000000
knowledge     0.000000   0.414541   0.000000
like          0.000000   0.000000   0.479528
programming   0.363831   0.000000   0.000000
reading       0.000000   0.000000   0.479528
skills        0.553405   0.315269   0.000000
statistics    0.276703   0.315269   0.000000
travelling    0.000000   0.000000   0.479528

Frequency Chart

This visualization presents a bar chart whose length corresponds to the frequency a particular word occurred. Let’s plot a frequency chart for Doc_1.txt file. See Listing 5-21.

Listing 5-21. Example code for frequency chart

words = df.index
freq = df.ix[:,0].sort(ascending=False, inplace=False)

pos = np.arange(len(words))
width=1.0
ax=plt.axes(frameon=True)
ax.set_xticks(pos)
ax.set_xticklabels(words, rotation='vertical', fontsize=9)
ax.set_title('Word Frequency Chart')
ax.set_xlabel('Words')
ax.set_ylabel('Frequency')
plt.bar(pos, freq, width, color='b')
plt.show()
#----output----

Word Cloud

This is a visual representation of text data, which is helpful to get a high-level understanding about the important keywords from data in terms of its occurrence. ‘WordCloud’ package can be used to generate words whose font size relates to its frequency. See Listing 5-22.

Listing 5-22. Example code for wordcloud

from wordcloud import WordCloud

# Read the whole text.
text = open('Data/Text_Files/Doc_1.txt').read()

# Generate a word cloud image
wordcloud = WordCloud().generate(text)

# Display the generated image:
# the matplotlib way:
import matplotlib.pyplot as plt
plt.imshow(wordcloud.recolor(random_state=2017))
plt.title('Most Frequent Words')
plt.axis("off")
plt.show()
#----output----

From the above chart we can see that ‘skills’ appear the most number of times comparatively.

Lexical Dispersion Plot

This plot is helpful to determine the location of a word in a sequence of text sentences. On the x-axis you’ll have word offset numbers and on the y-axis each row is a representation of the entire text and the marker indicates an instance of the word of interest. See Listing 5-23.

Listing 5-23. Example code for lexical dispersion plot

from nltk import word_tokenize

def dispersion_plot(text, words):
    words_token = word_tokenize(text)
    points = [(x,y) for x in range(len(words_token)) for y in range(len(words)) if words_token[x] == words[y]]

    if points:
        x,y=zip(*points)
    else:
        x=y=()

    plt.plot(x,y,"rx",scalex=.1)
    plt.yticks(range(len(words)),words,color="b")
    plt.ylim(-1,len(words))
    plt.title("Lexical Dispersion Plot")
    plt.xlabel("Word Offset")
    plt.show()

text = 'statistics skills, and programming skills are equally important for analytics. statistics skills, and domain knowledge are important for analytics'

dispersion_plot(text, ['statistics', 'skills', 'and', 'important'])
#----output----

Co-occurrence Matrix

Calculating the co-occurrence between words in a sequence of text will be helpful matrices to explain the relationship between words. A co-occurrence matrix tells us how many times every word has co-occurred with the current word. Further plotting this matrix into a heat map is a powerful visual tool to spot the relationships between words efficiently. See Listing 5-24.

Listing 5-24. Example code for co-occurrence matrix

import statsmodels.api as sm
import scipy.sparse as sp

# default unigram model
count_model = CountVectorizer(ngram_range=(1,1))
docs_unigram = count_model.fit_transform(docs.get('docs'))

# co-occurrence matrix in sparse csr format
docs_unigram_matrix = (docs_unigram.T * docs_unigram)

# fill same word cooccurence to 0
docs_unigram_matrix.setdiag(0)

# co-occurrence matrix in sparse csr format
docs_unigram_matrix = (docs_unigram.T * docs_unigram) docs_unigram_matrix_diags = sp.diags(1./docs_unigram_matrix.diagonal())

# normalized co-occurence matrix
docs_unigram_matrix_norm = docs_unigram_matrix_diags * docs_unigram_matrix

# Convert to a dataframe
df = pd.DataFrame(docs_unigram_matrix_norm.todense(), index = count_model.get_feature_names())
df.columns = count_model.get_feature_names()

# Plot
sm.graphics.plot_corr(df, title='Co-occurrence Matrix', xnames=list(df.index))
plt.show()
#----output----

Latent Semantic Analysis (LSA)

LSA is a mathematical method that tries to bring out latent relationships within a collection of documents. Rather than looking at each document isolated from the others, it looks at all the documents as a whole and the terms within them to identify relationships. Let’s perform LSA by running SVD on the data to reduce the dimensionality.

SVD of matrix A = U * ∑ * VT              

r = rank of matrix X
U = column orthonormal m * r matrix
∑ = diagonal r * r matrix with singular value sorted in descending order
V = column orthonormal r * n matrix

In our case we have 3 topics, 2768 documents and 35311 word vocabulary.

* Original matrix = 2768*35311 ∼ 108              
* SVD = 3*2768 + 3 + 3*35311 ∼ 105.3              

Resulted SVD is taking approximately 460 times less space than original matrix.

Note

“Latent Semantic Analysis (LSA)” and “Latent Semantic Indexing (LSI)” is the same thing, with the latter name being used sometimes when referring specifically to indexing a collection of documents for search (“Information Retrieval”). See Figure 5-6 and Listing 5-27.

Figure 5-6. Singular Value Decomposition

Listing 5-27. Example code for LSA through SVD

from sklearn.decomposition import TruncatedSVD

# Lets reduce the dimensionality to 2000
svd = TruncatedSVD(2000)
lsa = make_pipeline(svd, Normalizer(copy=False))

X = lsa.fit_transform(X)

explained_variance = svd.explained_variance_ratio_.sum()
print("Explained variance of the SVD step: {}%".format(int(explained_variance * 100)))
#----output----
Explained variance of the SVD step: 95%

Let’s run k-means clustering on the SVD output as shown in Listing 5-28.

Listing 5-28. k-means clustering on SVD dataset

from __future__ import print_function

km = KMeans(n_clusters=3, init='k-means++', max_iter=100, n_init=1)

# Scikit learn provides MiniBatchKMeans to run k-means in batch mode suitable for a very large corpus
# km = MiniBatchKMeans(n_clusters=5, init='k-means++', n_init=1, init_size=1000, batch_size=1000)

print("Clustering sparse data with %s" % km)
km.fit(X)

print("Top terms per cluster:")
original_space_centroids = svd.inverse_transform(km.cluster_centers_)
order_centroids = original_space_centroids.argsort()[:, ::-1]

terms = vectorizer.get_feature_names()
for i in range(3):
    print("Cluster %d:" % i, end='')
    for ind in order_centroids[i, :10]:
        print(' %s' % terms[ind], end='')
    print()
#----output----
Top terms per cluster:
Cluster 0: edu graphics university god subject lines organization com posting uk
Cluster 1: com bike edu dod ca writes article sun like organization
Cluster 2: keith sgi livesey caltech com solntze wpd jon edu sandvik

Latent Dirichlet Allocation (LDA)

LDA was presented by David Blei, Andrew Ng, and Michael I.J in 2003 as a graphical model. See Figure 5-7.

Figure 5-7. LDA graph model

LDA is given by

Where, F(z) = word distribution for topic,

a = Dirichlet parameter prior the per-document topic distribution,

b = Dirichlet parameter prior the per-document word distribution,

q(d) = topic distribution for a document

LDA’s objective is to maximize separation between means of projected topics and minimize variance within each projected topic. So LDA defines each topic as a bag of words by carrying out three steps described below.

Step 1: Initialize k clusters and assign each word in the document to one of the k topics.

Step 2: Re-assign word to new topic based on a) how is the proportion of words for a document to a topic, and b) how is the proportion of a topic widespread across all documents.

Step 3: Repeat step 2 until coherent topics result. See Figure 5-8 and Listing 5-29.

Figure 5-8. Latent Dirichlet Allocation (LDA)

Listing 5-29. Example code for LDA

from sklearn.decomposition import LatentDirichletAllocation

# continuing with the 20 newsgroup dataset and 3 topics
total_topics = 3
lda = LatentDirichletAllocation(n_topics=total_topics,
                                max_iter=100,
                                learning_method='online',
                                learning_offset=50.,
                                random_state=2017)
lda.fit(X)

feature_names = np.array(vectorizer.get_feature_names())

for topic_idx, topic in enumerate(lda.components_):
    print("Topic #%d:" % topic_idx)
    print(" ".join([feature_names[i] for i in topic.argsort()[:-20 - 1:-1]]))
#----output----
Topic #0:
edu com writes subject lines organization article posting university nntp host don like god uk ca just bike know graphics
Topic #1:
anl elliptical maier michael_maier qmgate separations imagesetter 5298 unscene appreshed linotronic l300 iici amnesia glued veiw halftone 708 252 dot
Topic #2:
hl7204 eehp22 raoul vrrend386 qedbbs choung qed daruwala ims kkt briarcliff kiat philabs col op_rows op_cols keeve 9327 lakewood gans

Non-negative Matrix Factorization

NMF is a decomposition method for multivariate data, and is given by V = MH, where V is the product of matrices W and H. W is a matrix of word rank in the features, and H is the coefficient matrix with each row being a feature. The three matrices have no negative elements. See Listing 5-30.

Listing 5-30. Example code for Non-negative matrix factorization

from sklearn.decomposition import NMF

nmf = NMF(n_components=total_topics, random_state=2017, alpha=.1, l1_ratio=.5)
nmf.fit(X)

for topic_idx, topic in enumerate(nmf.components_):
    print("Topic #%d:" % topic_idx)
    print(" ".join([feature_names[i] for i in topic.argsort()[:-20 - 1:-1]]))
#----output----
Topic #0:
edu com god writes article don subject lines organization just university bike people posting like know uk ca think host
Topic #1:
sgi livesey keith solntze wpd jon caltech morality schneider cco moral com allan edu objective political cruel atheists gap writes
Topic #2:
sun east green ed egreen com cruncher microsystems ninjaite 8302 460 rtp 0111 nc 919 grateful drinking pixel biker showed

Content-Based Filtering

This type of system focuses on the similarity attributes of the items to give you recommendations. This is best understood with an example, so if a user has purchased items of a particular category then other similar items from the same category are recommended to the user (refer to Figure 5-10).

An item-based similarity recommendation algorithm can be represented as shown here:

Collaborative Filtering (CF)

CF focuses on the similarity attribute of the users, that is,it finds people with similar tastes based on a similarity measure from the large group of users. There are two types of CF implementation in practice: memory-based and model-based.

The memory-based recommendation is mainly based on the similarity algorithm; the algorithm looks at items liked by similar people to create a ranked list of recommendations. You can then sort the ranked list to recommend the top n items to the user.

The user-based similarity recommendation algorithm can be represented as:

Let’s consider an example dataset of movie ratings (Figure 5-11) and apply item- and user-based recommendations to get a better understanding. See Listing 5-37.

Figure 5-11. Movie rating sample dataset

Listing 5-37. Example code for recommender system

import numpy as np
import pandas as pd

df = pd.read_csv('Data/movie_rating.csv')

n_users = df.userID.unique().shape[0]
n_items = df.itemID.unique().shape[0]
print '\nNumber of users = ' + str(n_users) + ' | Number of movies = ' + str(n_items)
#----output----
Number of users = 7 | Number of movies = 6

# Create user-item similarity matrices
df_matrix = np.zeros((n_users, n_items))
for line in df.itertuples():
    df_matrix[line[1]-1, line[2]-1] = line[3]

from sklearn.metrics.pairwise import pairwise_distances

user_similarity = pairwise_distances(df_matrix, metric='cosine')
item_similarity = pairwise_distances(df_matrix.T, metric='cosine')

# Top 3 similar users for user id 7
print "Similar users for user id 7: \n", pd.DataFrame(user_similarity).loc[6,pd.DataFrame(user_similarity).loc[6,:] > 0].sort_values(ascending=False)[0:3]
#----output----
Similar users for user id 7:
3    8.000000
0    6.062178
5    5.873670

# Top 3 similar items for item id 6
print "Similar items for item id 6: \n", pd.DataFrame(item_similarity).loc[5,pd.DataFrame(item_similarity).loc[5,:] > 0].sort_values(ascending=False)[0:3]
#----output----
0    6.557439
2    5.522681
3    4.974937

Let’s build the user-based predict and item-based prediction for forumla as a function. Apply this function to predict ratings and use root mean squared error (RMSE) to evaluate the model performance.

See Listing 5-38.

Listing 5-38. Example code for recommender system & accuracy evaluation

# Function for item based rating prediction
def item_based_prediction(rating_matrix, similarity_matrix):
    return rating_matrix.dot(similarity_matrix) / np.array([np.abs(similarity_matrix).sum(axis=1)])

# Function for user based rating prediction
def user_based_prediction(rating_matrix, similarity_matrix):
    mean_user_rating = rating_matrix.mean(axis=1)
    ratings_diff = (rating_matrix - mean_user_rating[:, np.newaxis])
    return mean_user_rating[:, np.newaxis] + similarity_matrix.dot(ratings_diff) / np.array([np.abs(similarity_matrix).sum(axis=1)]).T

item_based_prediction = item_based_prediction(df_matrix, item_similarity)
user_based_prediction = user_based_prediction(df_matrix, user_similarity)

# Calculate the RMSE
from sklearn.metrics import mean_squared_error
from math import sqrt
def rmse(prediction, actual):
    prediction = prediction[actual.nonzero()].flatten()
    actual = actual[actual.nonzero()].flatten()
    return sqrt(mean_squared_error(prediction, actual))

print 'User-based CF RMSE: ' + str(rmse(user_based_prediction, df_matrix))
print 'Item-based CF RMSE: ' + str(rmse(item_based_prediction, df_matrix))
#----output----
User-based CF RMSE: 1.0705767849
Item-based CF RMSE: 1.37392288971

y_user_based = pd.DataFrame(user_based_prediction)

# Predictions for movies that the user 6 hasn't rated yet
predictions = y_user_based.loc[6,pd.DataFrame(df_matrix).loc[6,:] == 0]
top = predictions.sort_values(ascending=False).head(n=1)
recommendations = pd.DataFrame(data=top)
recommendations.columns = ['Predicted Rating']
print recommendations
#----output----
   Predicted Rating
1          2.282415

y_item_based = pd.DataFrame(item_based_prediction)

# Predictions for movies that the user 6 hasn't rated yet
predictions = y_item_based.loc[6,pd.DataFrame(df_matrix).loc[6,:] == 0]
top = predictions.sort_values(ascending=False).head(n=1)
recommendations = pd.DataFrame(data=top)
recommendations.columns = ['Predicted Rating']
print recommendations
#----output----
   Predicted Rating
5          2.262497

Based on user based the recommended Intersellar is recommended (5th index). Based on item based the recommended movie is Avengers Assemble (index number 1).

Model-based CF is based on matrix factorization (MF) such as Singular Value Decomposition (SVD) and Non-nagative matrix factorization (NMF) etc. Let’s look how to implement using SVD.

See Listing 5-39.

Listing 5-39. Example code for recommender system using SVD

# calculate sparsity level
sparsity=round(1.0-len(df)/float(n_users*n_items),3)
print 'The sparsity level of is ' +  str(sparsity*100) + '%'

import scipy.sparse as sp
from scipy.sparse.linalg import svds

# Get SVD components from train matrix. Choose k.
u, s, vt = svds(df_matrix, k = 5)
s_diag_matrix=np.diag(s)
X_pred = np.dot(np.dot(u, s_diag_matrix), vt)
print 'User-based CF MSE: ' + str(rmse(X_pred, df_matrix))
#----output----
The sparsity level of is 0.0%
User-based CF MSE: 0.015742898995

Note that, in our case the data set is small, hence sparsity level is 0%. I recommend you to try this method on the MovieLens 100k dataset which you can download from https://grouplens.org/datasets/movielens/100k/