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Text classification with NLTK and Scikit-Learn

Summary:

We have collected data from two different categories: Hotels and Travel & Health and medical, cleaned the text and transformed it to a suitable representation, in this case we implemented a Bag of Words model. Both categories contain an imbalanced amount of classes so we have to evaluate them using Precision-Recall curves and Avg. Precision. We test different classifiers and finally train the models using a Naive Bayes model (as it perfomes the best compared to rest). We reach an average precision of 95%

# from standard python library
import re, string 
import os
import urllib.request
import warnings
warnings.filterwarnings('ignore')

# third party libraries: BeautifulSoup, Numpy, Pandas, NLTK, Sklearn
from bs4 import BeautifulSoup

import numpy as np
import pandas as pd

from nltk.corpus import stopwords
from nltk.stem import PorterStemmer
from nltk.stem.wordnet import WordNetLemmatizer

import sklearn
from sklearn.model_selection import cross_val_score, cross_val_predict
from joblib import load, dump
from sklearn.linear_model import SGDClassifier
from sklearn.naive_bayes import GaussianNB
from sklearn.ensemble import BaggingClassifier
from sklearn.feature_selection import SelectFromModel
from sklearn.base import clone
from sklearn.model_selection import train_test_split
from sklearn import ensemble, naive_bayes, svm, tree
from sklearn.feature_selection import SelectKBest
from sklearn.feature_selection import chi2
from sklearn.metrics import roc_curve, auc, classification_report, precision_recall_curve, average_precision_score, f1_score
from sklearn import preprocessing

%matplotlib inline
import matplotlib.pyplot as plt

We are thinking of testing different classifiers with our datasets, we will create a class to handle all the tests at once and return the best classifier.

class TestClassifiers(object):

    def __init__(self, X, y, classifiers=None, scoring="accuracy"):
        
        self.X = X
        self.y = y
        
        if classifiers is None:
            self.classifiers = []
        self.classifiers = classifiers
        
        self.scoring = scoring
        
        # attribute asigned in call_fit method
        self.scores = []
        self.preds = []

    
    def cv_on_classifiers(self, folds=5):
        """ Apply cross validation on all classifiers
        """

        for classifier in self.classifiers:
            print("Cross-Validation using {} Classifier".format(type(classifier).__name__))
            score = cross_val_score(classifier, self.X, self.y, scoring=self.scoring, cv=folds)
            print("Scores:", score, "Mean score:", np.mean(score))
            self.scores.append(np.mean(score))
    
    def cv_pred_on_classifiers(self, folds=5, method='predict'):
        """ Apply cross validation predict on all classifiers
        """

        for classifier in self.classifiers:
            print("Predictions using Cross-Validation with {} Classifier".format(type(classifier).__name__))
            preds = cross_val_predict(classifier, self.X, self.y, cv=folds, n_jobs=5, method='predict')
            self.preds.append(preds)


    def fit_on_classifiers(self, prefix="", dump_=True):
        """ Apply fit method to all classifiers
        """

        for classifier in self.classifiers:
            print("Fitting {} Classifier".format(type(classifier).__name__))
            classifier.fit(self.X, self.y)
            print("Finished training classifier ", str(classifier))
            
            if dump_:
                dump(classifier, "../models/{}_{}.joblib".format(type(classifier).__name__, prefix))
    

    def best_classifier(self):
        """ Returns the classifier with the max score
        """
        print("Best classifier: \n")
        max_ = self.scores.index(np.max(self.scores))
        return self.classifiers[max_]


    def load_classifiers(self):
        """ Load classifiers from file
        """
        for classifier in self.classifiers:
            classifier = load("models/{}.joblib".format(type(classifier).__name__))

Let's leave this class aside for a second, we will come back to it after downloading and processing our data. We will focus on only two categories out of the 5, "Health and medical" and "Hotels and travel":

def parse_html(url):
    response = urllib.request.urlopen(url)
    html_doc = response.read()
    return BeautifulSoup(html_doc, 'html.parser')

def explore_and_download(url):
    # Fetch the html file: http://mlg.ucd.ie/modules/yalp/
    soup = parse_html(url)
    all_reviews = []
    all_stars = []
    # links at home page
    for i, link in enumerate(soup.find_all('a')):
        #Category: Automotive
        #Category: Bars
        #Category: Health and medical
        #Category: Hotels and travel
        #Category: Restaurant
        if i == 2 or i == 3: # 'Health & Medical' and 'Hotels & Travel'
            
            soup = parse_html(url+link.get('href'))
            # links level 2 (businesses)
            for link_2 in soup.find_all('a'):
                # List of 122 businesses in the category Health and medical
                # List of all 89 businesses in the category Hotels and travel
                print(link_2.get('href'))
                # access link & get reviews
                soup_2 = parse_html(url + link_2.get('href'))
                # find the scores:
                for p in soup_2.find_all('img'):
                    try: #the first entry has no attribute 'alt'
                        all_stars.append(p['alt'])
                    except:
                        pass
                # find the reviews:
                for p in soup_2.find_all('p'):
                    if p['class'][0] == 'text':
                        all_reviews.append(p.get_text())

            # concatenate and save the results
            results = np.concatenate((np.array(all_stars).reshape(-1,1), np.array(all_reviews).reshape(-1,1)), axis=1)
            pd.DataFrame(results, columns=['rate','review']).to_csv('../csv/' + link.get_text()[10:] + '.csv', index=False)

Let's see what our Health and medical dataset looks like:

base_url = "http://mlg.ucd.ie/modules/yalp/"

if not os.path.isfile('../csv/Health and medical.csv'):
    explore_and_download(base_url)
    
health = pd.read_csv('../csv/Health and medical.csv')
health
rate review
0 5-star I have so many good things to say about this p...
1 5-star I found them to be highly skilled and an exper...
2 5-star Where do I even begin? This office has been so...
3 5-star I went in because I had toothache and needed a...
4 5-star Found a new dental office. This place is amazi...
5 5-star Dr. Carlos is always on top of things, I've ne...
6 5-star Dr. Carlos and the staff were very friendly. T...
7 5-star Love these guys! Had a chip in my tooth and no...
8 5-star I just found this office in Scottsdale and the...
9 5-star Dr. Mandap has been my dentist for many years ...
10 5-star A bit of a drive on the freeways but this plac...
11 1-star Wow. Do not order from here. I ordered an item...
12 1-star I was searching google for diabetic shoes for ...
13 5-star Am I reviewing the same company as everyone el...
14 1-star This company is terrible! My mom purchased a p...
15 1-star Horrible Experience. I ordered an item and req...
16 1-star Ordered item in April 2015. Never arrived. The...
17 1-star Terrible online service! I ordered one item an...
18 1-star I want to let everyone know to not make purcha...
19 1-star Horrible customer service ... Ordered an item ...
20 1-star I purchased a calf sleeve from this company to...
21 1-star The website descriptions and advertising is pu...
22 1-star Do not deal with this company. I ordered some ...
23 1-star they had the best price around for the item i ...
24 1-star I should have looked at the reviews before ord...
25 1-star DON"T BUY FROM THIS COMPANY. my order never ar...
26 1-star There are only two positive reviews (read: shi...
27 1-star Take your business else where. Notice how the ...
28 5-star I found ActiveForever after a family incident....
29 1-star Ordered a product online and paid for for expe...
... ... ...
1420 5-star Yuliana, the owner, is professional, knowledge...
1421 1-star Everything was great until they burned my cupi...
1422 5-star Let me start by saying that I'm used to paying...
1423 5-star Yuliya is the best at her job. I highly recomm...
1424 5-star I have had about 4 session of hair removal and...
1425 5-star Just had my facial/microderm treatment. It was...
1426 5-star This is the best laser hair removal in Toronto...
1427 5-star I love it here ! Yulia makes the process of la...
1428 5-star This place is one of Toronto's best-kept, imma...
1429 5-star Yuilya is so kind and professional. She genuin...
1430 5-star The customer service is exceptional. I loved t...
1431 5-star Yuliya is great! She's incredibly sweet and ha...
1432 5-star I have never had any kind if laser treatments ...
1433 5-star YS Canadian Laser Spa is wonderful. Yuliya is ...
1434 5-star Yuliya is amazing! I've had multiple sessions ...
1435 5-star Yuliya is such a nice person and I felt so inc...
1436 5-star I went for the first time to do laser hair rem...
1437 5-star I had a wonderful spa experience at Canadian L...
1438 5-star A wonderful treatment, makes you leave feeling...
1439 4-star I did a lot of research for different dental o...
1440 5-star I came from the US to do my teeth here. Wonder...
1441 5-star The staff is amazing, obviously customer servi...
1442 5-star Gelareh did such an amazing cleaning for me th...
1443 5-star Friendly staff that is both very professional ...
1444 5-star Always a great place to get all your supplemen...
1445 1-star WAY OVERPRICED. Go to Healthy Planet, or other...
1446 4-star I'm surprised at the negative reviews. I go he...
1447 1-star I've came in to this store twice now to purcha...
1448 1-star Most definitely not impressed with this place....
1449 2-star If a place like this can afford the rent on th...

1450 rows Ă— 2 columns

Now let's take a look at Hotels and travel:

if not os.path.isfile('../csv/Hotels and travel.csv'):
    explore_and_download(base_url)

hotels = pd.read_csv('../csv/Hotels and travel.csv')
hotels
rate review
0 5-star I have so many good things to say about this p...
1 5-star I found them to be highly skilled and an exper...
2 5-star Where do I even begin? This office has been so...
3 5-star I went in because I had toothache and needed a...
4 5-star Found a new dental office. This place is amazi...
5 5-star Dr. Carlos is always on top of things, I've ne...
6 5-star Dr. Carlos and the staff were very friendly. T...
7 5-star Love these guys! Had a chip in my tooth and no...
8 5-star I just found this office in Scottsdale and the...
9 5-star Dr. Mandap has been my dentist for many years ...
10 5-star A bit of a drive on the freeways but this plac...
11 1-star Wow. Do not order from here. I ordered an item...
12 1-star I was searching google for diabetic shoes for ...
13 5-star Am I reviewing the same company as everyone el...
14 1-star This company is terrible! My mom purchased a p...
15 1-star Horrible Experience. I ordered an item and req...
16 1-star Ordered item in April 2015. Never arrived. The...
17 1-star Terrible online service! I ordered one item an...
18 1-star I want to let everyone know to not make purcha...
19 1-star Horrible customer service ... Ordered an item ...
20 1-star I purchased a calf sleeve from this company to...
21 1-star The website descriptions and advertising is pu...
22 1-star Do not deal with this company. I ordered some ...
23 1-star they had the best price around for the item i ...
24 1-star I should have looked at the reviews before ord...
25 1-star DON"T BUY FROM THIS COMPANY. my order never ar...
26 1-star There are only two positive reviews (read: shi...
27 1-star Take your business else where. Notice how the ...
28 5-star I found ActiveForever after a family incident....
29 1-star Ordered a product online and paid for for expe...
... ... ...
2850 5-star Classic old hotel with all the right upgrades ...
2851 5-star The Ritz in Montreal is beautiful. It is locat...
2852 5-star For my 300th review on Yelp....I decided to wr...
2853 5-star The staff at this amazing hotel go above and b...
2854 5-star I recently attended an executive conference at...
2855 5-star I have been to many Ritz all over the world an...
2856 5-star The Ritz was a perfect place to stay in Montre...
2857 3-star I brought my mum here for her 70th birthday a ...
2858 5-star This is a review only on the meeting room, not...
2859 4-star Oh the Ritz darling, what a fabulous experienc...
2860 4-star *This review is for my High Tea experience onl...
2861 5-star Beautiful hotel with great amenities. They acc...
2862 5-star Very nice medium sized luxury 5 star hotel wit...
2863 5-star As a frequent business traveler staying in top...
2864 5-star Beautiful hotel, perfect location (food, shopp...
2865 5-star After learning about the hotel's new renovatio...
2866 5-star Thé royal dans le "Palm court", le foyer consu...
2867 5-star Simply fantastic! One of the best, if not the ...
2868 5-star Perfection in every way! Beautiful rooms, grea...
2869 5-star This is the standard of Ritz Carlton. The tech...
2870 5-star This was the most amazing hotel experience I'v...
2871 5-star Recently renovated. Beautiful rooms with high ...
2872 5-star Hey, it's the Ritz, what can I say? This hotel...
2873 5-star Fabulous service. We stayed for 4 nights to ce...
2874 4-star The Ritz on Sherbrooke really does not look li...
2875 4-star Always wanted to try out a proper British high...
2876 5-star I have traveled to some of the most beautiful ...
2877 5-star Simon the concierge and victor the front desk ...
2878 5-star What I like about this hotel: great location; ...
2879 5-star OMG!!!! After being closed for 4 years for a r...

2880 rows Ă— 2 columns

Now let's classify the stars rating into two groups, 1-3 stars: negative and 4-5: positive

if not os.path.isfile('../csv/Health and medical (classified).csv'):
    classify_stars('../csv/Health and medical.csv', '../csv/Health and medical (classified).csv')
if not os.path.isfile('../csv/Hotels and travel (classified).csv'):
    classify_stars('../csv/Hotels and travel.csv', '../csv/Hotels and travel (classified).csv')

health = pd.read_csv('../csv/Hotels and travel (classified).csv', index_col=0)
hotels = pd.read_csv('../csv/Health and medical (classified).csv', index_col=0)
health, hotels
(        rate                                             review     class
 0     5-star  I have so many good things to say about this p...  positive
 1     5-star  I found them to be highly skilled and an exper...  positive
 2     5-star  Where do I even begin? This office has been so...  positive
 3     5-star  I went in because I had toothache and needed a...  positive
 4     5-star  Found a new dental office. This place is amazi...  positive
 5     5-star  Dr. Carlos is always on top of things, I've ne...  positive
 6     5-star  Dr. Carlos and the staff were very friendly. T...  positive
 7     5-star  Love these guys! Had a chip in my tooth and no...  positive
 8     5-star  I just found this office in Scottsdale and the...  positive
 9     5-star  Dr. Mandap has been my dentist for many years ...  positive
 10    5-star  A bit of a drive on the freeways but this plac...  positive
 11    1-star  Wow. Do not order from here. I ordered an item...  negative
 12    1-star  I was searching google for diabetic shoes for ...  negative
 13    5-star  Am I reviewing the same company as everyone el...  positive
 14    1-star  This company is terrible! My mom purchased a p...  negative
 15    1-star  Horrible Experience. I ordered an item and req...  negative
 16    1-star  Ordered item in April 2015. Never arrived. The...  negative
 17    1-star  Terrible online service! I ordered one item an...  negative
 18    1-star  I want to let everyone know to not make purcha...  negative
 19    1-star  Horrible customer service ... Ordered an item ...  negative
 20    1-star  I purchased a calf sleeve from this company to...  negative
 21    1-star  The website descriptions and advertising is pu...  negative
 22    1-star  Do not deal with this company. I ordered some ...  negative
 23    1-star  they had the best price around for the item i ...  negative
 24    1-star  I should have looked at the reviews before ord...  negative
 25    1-star  DON"T BUY FROM THIS COMPANY. my order never ar...  negative
 26    1-star  There are only two positive reviews (read: shi...  negative
 27    1-star  Take your business else where. Notice how the ...  negative
 28    5-star  I found ActiveForever after a family incident....  positive
 29    1-star  Ordered a product online and paid for for expe...  negative
 ...      ...                                                ...       ...
 2850  5-star  Classic old hotel with all the right upgrades ...  positive
 2851  5-star  The Ritz in Montreal is beautiful. It is locat...  positive
 2852  5-star  For my 300th review on Yelp....I decided to wr...  positive
 2853  5-star  The staff at this amazing hotel go above and b...  positive
 2854  5-star  I recently attended an executive conference at...  positive
 2855  5-star  I have been to many Ritz all over the world an...  positive
 2856  5-star  The Ritz was a perfect place to stay in Montre...  positive
 2857  3-star  I brought my mum here for her 70th birthday a ...  negative
 2858  5-star  This is a review only on the meeting room, not...  positive
 2859  4-star  Oh the Ritz darling, what a fabulous experienc...  positive
 2860  4-star  *This review is for my High Tea experience onl...  positive
 2861  5-star  Beautiful hotel with great amenities. They acc...  positive
 2862  5-star  Very nice medium sized luxury 5 star hotel wit...  positive
 2863  5-star  As a frequent business traveler staying in top...  positive
 2864  5-star  Beautiful hotel, perfect location (food, shopp...  positive
 2865  5-star  After learning about the hotel's new renovatio...  positive
 2866  5-star  Thé royal dans le "Palm court", le foyer consu...  positive
 2867  5-star  Simply fantastic! One of the best, if not the ...  positive
 2868  5-star  Perfection in every way! Beautiful rooms, grea...  positive
 2869  5-star  This is the standard of Ritz Carlton. The tech...  positive
 2870  5-star  This was the most amazing hotel experience I'v...  positive
 2871  5-star  Recently renovated. Beautiful rooms with high ...  positive
 2872  5-star  Hey, it's the Ritz, what can I say? This hotel...  positive
 2873  5-star  Fabulous service. We stayed for 4 nights to ce...  positive
 2874  4-star  The Ritz on Sherbrooke really does not look li...  positive
 2875  4-star  Always wanted to try out a proper British high...  positive
 2876  5-star  I have traveled to some of the most beautiful ...  positive
 2877  5-star  Simon the concierge and victor the front desk ...  positive
 2878  5-star  What I like about this hotel: great location; ...  positive
 2879  5-star  OMG!!!! After being closed for 4 years for a r...  positive
 
 [2880 rows x 3 columns],
         rate                                             review     class
 0     5-star  I have so many good things to say about this p...  positive
 1     5-star  I found them to be highly skilled and an exper...  positive
 2     5-star  Where do I even begin? This office has been so...  positive
 3     5-star  I went in because I had toothache and needed a...  positive
 4     5-star  Found a new dental office. This place is amazi...  positive
 5     5-star  Dr. Carlos is always on top of things, I've ne...  positive
 6     5-star  Dr. Carlos and the staff were very friendly. T...  positive
 7     5-star  Love these guys! Had a chip in my tooth and no...  positive
 8     5-star  I just found this office in Scottsdale and the...  positive
 9     5-star  Dr. Mandap has been my dentist for many years ...  positive
 10    5-star  A bit of a drive on the freeways but this plac...  positive
 11    1-star  Wow. Do not order from here. I ordered an item...  negative
 12    1-star  I was searching google for diabetic shoes for ...  negative
 13    5-star  Am I reviewing the same company as everyone el...  positive
 14    1-star  This company is terrible! My mom purchased a p...  negative
 15    1-star  Horrible Experience. I ordered an item and req...  negative
 16    1-star  Ordered item in April 2015. Never arrived. The...  negative
 17    1-star  Terrible online service! I ordered one item an...  negative
 18    1-star  I want to let everyone know to not make purcha...  negative
 19    1-star  Horrible customer service ... Ordered an item ...  negative
 20    1-star  I purchased a calf sleeve from this company to...  negative
 21    1-star  The website descriptions and advertising is pu...  negative
 22    1-star  Do not deal with this company. I ordered some ...  negative
 23    1-star  they had the best price around for the item i ...  negative
 24    1-star  I should have looked at the reviews before ord...  negative
 25    1-star  DON"T BUY FROM THIS COMPANY. my order never ar...  negative
 26    1-star  There are only two positive reviews (read: shi...  negative
 27    1-star  Take your business else where. Notice how the ...  negative
 28    5-star  I found ActiveForever after a family incident....  positive
 29    1-star  Ordered a product online and paid for for expe...  negative
 ...      ...                                                ...       ...
 1420  5-star  Yuliana, the owner, is professional, knowledge...  positive
 1421  1-star  Everything was great until they burned my cupi...  negative
 1422  5-star  Let me start by saying that I'm used to paying...  positive
 1423  5-star  Yuliya is the best at her job. I highly recomm...  positive
 1424  5-star  I have had about 4 session of hair removal and...  positive
 1425  5-star  Just had my facial/microderm treatment. It was...  positive
 1426  5-star  This is the best laser hair removal in Toronto...  positive
 1427  5-star  I love it here ! Yulia makes the process of la...  positive
 1428  5-star  This place is one of Toronto's best-kept, imma...  positive
 1429  5-star  Yuilya is so kind and professional. She genuin...  positive
 1430  5-star  The customer service is exceptional. I loved t...  positive
 1431  5-star  Yuliya is great! She's incredibly sweet and ha...  positive
 1432  5-star  I have never had any kind if laser treatments ...  positive
 1433  5-star  YS Canadian Laser Spa is wonderful. Yuliya is ...  positive
 1434  5-star  Yuliya is amazing! I've had multiple sessions ...  positive
 1435  5-star  Yuliya is such a nice person and I felt so inc...  positive
 1436  5-star  I went for the first time to do laser hair rem...  positive
 1437  5-star  I had a wonderful spa experience at Canadian L...  positive
 1438  5-star  A wonderful treatment, makes you leave feeling...  positive
 1439  4-star  I did a lot of research for different dental o...  positive
 1440  5-star  I came from the US to do my teeth here. Wonder...  positive
 1441  5-star  The staff is amazing, obviously customer servi...  positive
 1442  5-star  Gelareh did such an amazing cleaning for me th...  positive
 1443  5-star  Friendly staff that is both very professional ...  positive
 1444  5-star  Always a great place to get all your supplemen...  positive
 1445  1-star  WAY OVERPRICED. Go to Healthy Planet, or other...  negative
 1446  4-star  I'm surprised at the negative reviews. I go he...  positive
 1447  1-star  I've came in to this store twice now to purcha...  negative
 1448  1-star  Most definitely not impressed with this place....  negative
 1449  2-star  If a place like this can afford the rent on th...  negative
 
 [1450 rows x 3 columns])

Let's look at the classes distribution:

hotels.groupby('class')['class'].count()
class
negative     407
positive    1043
Name: class, dtype: int64
health.groupby('class')['class'].count()
class
negative    1044
positive    1836
Name: class, dtype: int64

ATENTION: Our classes are not evenly distributed, meaning that accuracy might not be a great indicator of a good performance, instead we will measure, precision and recall.

When to Use ROC vs. Precision-Recall Curves?

Generally, the use of ROC curves and precision-recall curves are as follows:

* ROC curves should be used when there are roughly equal numbers of observations for each class.

* Precision-Recall curves should be used when there is a moderate to large class imbalance.

The reason for this recommendation is that ROC curves present an optimistic picture of the model on datasets with a class imbalance.

As our machine learning techniques do not know how to process raw text, we need to transform it into a suitable representation. We will use the Bag of Word model.

We define a set of methods that together will create a pipeline of transformations:

def filter_words(raw_comments):
    """ Returns a filtered list
        Removes numbers and symbols from each comment
    """
    table = str.maketrans('', '', string.punctuation + string.digits)
    stripped = [comment.translate(table) for comment in raw_comments]
    return stripped

def lowercase_all(comments):
    """ Returns a list of lowercased words
    """
    return [comment.lower() for comment in comments]

def split_words(comments):
    """ Splits each comment as a list of strings, where each string is a word
    """
    return [re.split(r'\W+', comment) for comment in comments]

def flatten_words(comments):
    """ Returns a list of strings, where each string is a word
    """
    return [word for comment in comments for word in comment]

def remove_stopwords(words):
    """ Returns a list filter out stop words
    """
    stop_words = set(stopwords.words('english'))
    return [word for word in words if not word in stop_words]

def lemmatize(words):
    """ Lemma conversion
    """
    lem = WordNetLemmatizer()
    return [lem.lemmatize(word) for word in words]

def stemming(words):
    """ Linguistic normalization
    """
    ps = PorterStemmer()
    return [ps.stem(word) for word in words]

As we will use each word as features and eventually we want to test each classifier on a dataset other than the one it was trained on, we need to define a common set of features:

# take both files and concatenate them together:
if not os.path.isfile('../csv/concat_categories.csv'):    
    cat_1 = pd.read_csv('../csv/Hotels and travel (classified).csv')
    cat_2 = pd.read_csv('../csv/Health and medical (classified).csv')
    cats = pd.concat([cat_1, cat_2], ignore_index=True)
    cats.to_csv('../csv/concat_categories.csv')

Now, let's start our transformation pipeline for each of the files, we will use the concatenated files to define a vocabulary:

def create_vocabulary(path_read):
    
    data = pd.read_csv(path_read)
    # strip reviews and place them in a single list
    raw_comments = list(data['review'])

    # Create vocabulary
    filtered = filter_words(raw_comments)
    splitted = split_words(filtered)
    flattened = flatten_words(splitted)
    words = lowercase_all(flattened)
    words = remove_stopwords(words)
    words = lemmatize(words)
    words = stemming(words)
    return sorted(list(set(words)))


def document_term_matrix(path_read, path_write):
   
    # call and create vocabulary
    vocabulary =  create_vocabulary('../csv/concat_categories.csv')

    data = pd.read_csv(path_read)
    # strip reviews and place them in a single list
    raw_comments = list(data['review'])

    # Document-Term Matrix
    # Count frequency of words per comment
    filtered = filter_words(raw_comments)
    comments_as_words = lowercase_all(filtered)
    comments_as_words = split_words(comments_as_words)
    
    # allocate memory for efficiency, a matrix of 
    # rows = number of comments in the file and 
    # columns = number of words in vocabulary
    dtm = np.zeros((len(list(data['review'])), len(vocabulary)), dtype=np.int8, order='F')
    
    # for each comment in all the comments in the file
    for i, comment in enumerate(comments_as_words):
        # continue pipeline per comment
        cleaned_comment = remove_stopwords(comment)
        comment_lem = lemmatize(cleaned_comment)
        comment_stem = stemming(comment_lem)
        # count frequency of words in comment 
        uniques_count = pd.DataFrame(np.array(comment_stem).reshape(-1,1), columns=['words']).groupby(['words'])['words'].count()
        
        # assign the frequency of each word to the dtm matrix:
        for word in uniques_count.index:
            dtm[i, vocabulary.index(word)] = uniques_count[word]
    # save results    
    pd.DataFrame(dtm, columns=vocabulary).to_csv(path_write)
if not os.path.isfile('../csv/Hotels and travel dtm.csv'):
    document_term_matrix( '../csv/Hotels and travel (classified).csv', '../csv/Hotels and travel dtm.csv')

if not os.path.isfile('../csv/Health and medical dtm.csv'):
    document_term_matrix( '../csv/Health and medical (classified).csv', '../csv/Health and medical dtm.csv')

It is important to notice that this strategy produces a sparse matrix, which is not very ideal for memory purposes.

pd.read_csv('../csv/Hotels and travel dtm.csv', index_col=0)
Unnamed: 1 aa aaa aan aat abalo abbey abbrevi abdomen abdomin ... écrit égaux élaboré était étant été évident ête être über
0 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
3 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
5 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
6 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
7 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
8 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
9 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
10 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
11 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
12 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
13 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
14 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
15 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
16 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
17 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
18 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
19 1 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
20 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
21 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
22 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
23 1 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
24 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
25 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
26 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
27 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
28 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
29 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
2850 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2851 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2852 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2853 1 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2854 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2855 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2856 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2857 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2858 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2859 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2860 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2861 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2862 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2863 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2864 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2865 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2866 0 0 0 0 0 0 0 0 0 0 ... 0 1 0 0 0 1 0 0 0 0
2867 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2868 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2869 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2870 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2871 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2872 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2873 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2874 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2875 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2876 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2877 1 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2878 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
2879 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0

2880 rows Ă— 11197 columns

Our data is finally ready for training, we will be using our first defined class to test a set of three different classifiers, we expect naive bayes to do better than the rest because of the sparsity of the data:

def model_building(path_read_x, path_read_y, model_name):

    x_data = pd.read_csv(path_read_x, index_col=0)
    y_data = pd.read_csv(path_read_y, index_col=0)
    y_data = y_data['class']

    X_train, X_test_val, y_train, y_test_val = train_test_split(x_data, y_data,  test_size=0.3, random_state=1)
    X_test, X_val, y_test, y_val = train_test_split(X_test_val, y_test_val,  test_size=0.3, random_state=1)
    
    # configure models and leave default values as is:
    naive = naive_bayes.MultinomialNB()
    sgd = SGDClassifier(n_jobs=4)
    svmc = tree.DecisionTreeClassifier()
    
    clfs = [naive, sgd, svmc]
    # we will score the cross validation with roc_auc:
    # Compute Area Under the Receiver Operating Characteristic Curve (ROC AUC) from prediction scores
    test_clfs = TestClassifiers(X_train, y_train, classifiers=clfs, scoring='roc_auc')
    test_clfs.cv_on_classifiers(folds=5)
    best_classifier = test_clfs.best_classifier()
    
    
    # get predictions with best_classifier
    test_clf = TestClassifiers(X_train, y_train, classifiers=[best_classifier])
    test_clf.cv_pred_on_classifiers(method='predict_proba')
    print(best_classifier)
    
    #curve needs binary/numeric values, transform the labels to 0 and 1
    le = preprocessing.LabelEncoder()
    le.fit(['positive', 'negative'])
    y_pred = le.transform(test_clf.preds[0])
    y_train = le.transform(np.array(y_train))
    
    #print(np.array(y_train))
    precision, recall, thresholds = precision_recall_curve(y_train, y_pred)
    #fpr, tpr, thresholds = roc_curve(np.array(y_train_trans), np.array(y_pred_trans), pos_label=1)
    #area = auc(fpr, tpr)
    f1 = f1_score(y_train, y_pred )
    # calculate precision-recall AUC
    auc_ = auc(recall, precision)
    # calculate average precision score
    ap = average_precision_score(y_train, y_pred, pos_label=1)
    print('f1=%.3f auc=%.3f ap=%.3f' % (f1, auc_, ap))
    
    plt.figure() 
    lw = 2
    fig = plt.gcf()
    fig.set_size_inches(12, 10)
    plt.plot(recall, precision, color='darkorange',
             lw=lw, label='AUC (area = %0.2f)' % auc_)
    #plt.plot([0, 1], [0, 1], color='navy', lw=lw, linestyle='--')
    plt.xlim([0.0, 1.0])
    plt.ylim([0.0, 1.05])
    plt.xlabel('Recall')
    plt.ylabel('Precision')
    plt.title('Precision-Recall Curve (training data)',  fontsize=20)
    plt.legend(loc="lower right")
    
    return best_classifier

Test a Naive Bayes classifier, a SGD classifier and a Decision Tree classifier using 5 fold cross-validation, then return the best of them over the Hotels and Travel category

if not os.path.isfile('../models/MultinomialNB_model_ht.joblib'):
    best_classifier_1 = model_building('../csv/Hotels and travel dtm.csv', '../csv/Hotels and travel (classified).csv', 'model_ht')
Cross-Validation using MultinomialNB Classifier
Scores: [0.9316489  0.93571807 0.9454425  0.96894542 0.95606783] Mean score: 0.947564544410182
Cross-Validation using SGDClassifier Classifier
Scores: [0.92921437 0.94174616 0.93449921 0.95720721 0.9540673 ] Mean score: 0.9433468486251748
Cross-Validation using DecisionTreeClassifier Classifier
Scores: [0.73783393 0.75919449 0.77325119 0.77629836 0.79460784] Mean score: 0.7682371613619147
Best classifier: 

Predictions using Cross-Validation with MultinomialNB Classifier
MultinomialNB(alpha=1.0, class_prior=None, fit_prior=True)
f1=0.918 auc=0.942 ap=0.890

png

The best classifier was the Naive Bayes, with an avg. precision of 89%

We proceed to do the same for the Health and medical category:

if not os.path.isfile('../models/MultinomialNB_model_hm.joblib'):
    best_classifier_2 = model_building('../csv/Health and medical dtm.csv', '../csv/Health and medical (classified).csv', 'model_hm')
Cross-Validation using MultinomialNB Classifier
Scores: [0.97476568 0.95650084 0.95445806 0.91606585 0.97116078] Mean score: 0.954590242730113
Cross-Validation using SGDClassifier Classifier
Scores: [0.95085316 0.9513939  0.94688777 0.92093247 0.94766883] Mean score: 0.9435472242249461
Cross-Validation using DecisionTreeClassifier Classifier
Scores: [0.73317712 0.72632781 0.74194905 0.77319154 0.75606825] Mean score: 0.7461427541456381
Best classifier: 

Predictions using Cross-Validation with MultinomialNB Classifier
MultinomialNB(alpha=1.0, class_prior=None, fit_prior=True)
f1=0.942 auc=0.951 ap=0.904

png

Same as before, Naive Bayes is the best with avg. precision of 90.4%

These results are looking promissing.

Let's train the models on the training data and run them on the test data:

x_data = pd.read_csv('../csv/Hotels and travel dtm.csv', index_col=0)
y_data = pd.read_csv('../csv/Hotels and travel (classified).csv', index_col=0)
y_data = y_data['class']

X_train, X_test_val, y_train, y_test_val = train_test_split(x_data, y_data,  test_size=0.3, random_state=1)
X_test, X_val, y_test, y_val = train_test_split(X_test_val, y_test_val,  test_size=0.3, random_state=1)

#fit best classifier with filtered data
best_classifier_1.fit(X_train, y_train)
#produce some predictions
y_pred = best_classifier_1.predict(X_test)


#curve needs binary/numeric values, transform the labels to 0 and 1
le = preprocessing.LabelEncoder()
le.fit(['positive', 'negative'])
y_pred = le.transform(y_pred)
y_test = le.transform(y_test)

precision, recall, thresholds = precision_recall_curve(y_test, y_pred)
f1 = f1_score(y_test, y_pred )

# calculate precision-recall AUC
auc_ = auc(recall, precision)

# calculate average precision score
ap = average_precision_score(y_test, y_pred, pos_label=1)
print('f1=%.3f auc=%.3f ap=%.3f' % (f1, auc_, ap))
    

plt.figure() 
lw = 2
fig = plt.gcf()
fig.set_size_inches(12, 10)
plt.plot(recall, precision, color='darkorange',
         lw=lw, label='AUC (area = %0.2f)' % auc_)
#plt.plot([0, 1], [0, 1], color='navy', lw=lw, linestyle='--')
plt.xlim([0.0, 1.0])
plt.ylim([0.0, 1.05])
plt.xlabel('Recall')
plt.ylabel('Precision')
plt.title('PR Curve for HOTELS AND TRAVEL (test_set)',  fontsize=20)
plt.legend(loc="lower right")
f1=0.930 auc=0.949 ap=0.902





<matplotlib.legend.Legend at 0x2321f78c240>

png

We seem to be able to generalize from our training data, as we are getting about the same values in avg. precision = 90.2%

We run the same analysis on the health and medical data

x_data = pd.read_csv('../csv/Health and medical dtm.csv', index_col=0)
y_data = pd.read_csv('../csv/Health and medical (classified).csv', index_col=0)
y_data = y_data['class']

X_train, X_test_val, y_train, y_test_val = train_test_split(x_data, y_data,  test_size=0.3, random_state=1)
X_test, X_val, y_test, y_val = train_test_split(X_test_val, y_test_val,  test_size=0.3, random_state=1)

#fit best classifier with filtered data
best_classifier_2.fit(X_train, y_train)
#produce some predictions
y_pred = best_classifier_2.predict(X_test)

#encode the predictions
le = preprocessing.LabelEncoder()
le.fit(['positive', 'negative'])
y_test = le.transform(y_test)
y_pred = le.transform(y_pred)

precision, recall, thresholds = precision_recall_curve(y_test, y_pred)
f1 = f1_score(y_test, y_pred )

# calculate precision-recall AUC
auc_ = auc(recall, precision)

# calculate average precision score
ap = average_precision_score(y_test, y_pred, pos_label=1)
print('f1=%.3f auc=%.3f ap=%.3f' % (f1, auc_, ap))
    

plt.figure() 
lw = 2
fig = plt.gcf()
fig.set_size_inches(12, 10)
plt.plot(recall, precision, color='darkorange',
         lw=lw, label='AUC (area = %0.2f)' % auc_)
#plt.plot([0, 1], [0, 1], color='navy', lw=lw, linestyle='--')
plt.xlim([0.0, 1.0])
plt.ylim([0.0, 1.05])
plt.xlabel('Recall')
plt.ylabel('Precision')
plt.title('PR Curve for HEALTH AND MEDICAL (test_set)' , fontsize=20)
plt.legend(loc="lower right")
f1=0.945 auc=0.953 ap=0.908





<matplotlib.legend.Legend at 0x2321f7b00f0>

png

The results are really good, we are reaching an average precision of over 90% in both categories. For a dataset with such imbalance this is good news.

Let's see if our learning transfer from one category to the other.

x_data = pd.read_csv('../csv/Health and medical dtm.csv', index_col=0)
y_data = pd.read_csv('../csv/Health and medical (classified).csv', index_col=0)
y_data = y_data['class']

X_train, X_test_val, y_train, y_test_val = train_test_split(x_data, y_data,  test_size=0.3, random_state=1)
X_test, X_val, y_test, y_val = train_test_split(X_test_val, y_test_val,  test_size=0.3, random_state=1)

#fit best classifier with the whole training set (HEALTH AND MEDICAL)
best_classifier_2.fit(X_train, y_train)
dump(best_classifier_2, "../models/Naive_model_hm.joblib")

#produce some predictions using the other category as input
x_data = pd.read_csv('../csv/Hotels and travel dtm.csv', index_col=0)
y_data = pd.read_csv('../csv/Hotels and travel (classified).csv', index_col=0)
y_data = y_data['class']

y_pred = best_classifier_2.predict(x_data)

#encode the predictions
le = preprocessing.LabelEncoder()
le.fit(['positive', 'negative'])
y_test_ = le.transform(y_data)
y_pred_ = le.transform(y_pred)


precision, recall, thresholds = precision_recall_curve(y_test_, y_pred_)
f1 = f1_score(y_test_, y_pred_ )

# calculate precision-recall AUC
auc_ = auc(recall, precision)

# calculate average precision score
ap = average_precision_score(y_test_, y_pred_, pos_label=1)
print('f1=%.3f auc=%.3f ap=%.3f' % (f1, auc_, ap))
    
plt.figure() 
lw = 2
fig = plt.gcf()
fig.set_size_inches(12, 10)
plt.plot(recall, precision, color='darkorange',
         lw=lw, label='AUC (area = %0.2f)' % auc_)
#plt.plot([0, 1], [0, 1], color='navy', lw=lw, linestyle='--')
plt.xlim([0.0, 1.0])
plt.ylim([0.0, 1.05])
plt.xlabel('Recall')
plt.ylabel('Precision')
plt.title('PR-Curve HOTELS AND TRAVEL (with a model trained over HEALTH AND MEDICAL)', fontsize=20)
plt.legend(loc="lower right")
f1=0.933 auc=0.948 ap=0.900





<matplotlib.legend.Legend at 0x232243e2358>

png

print(classification_report(y_data, y_pred))
              precision    recall  f1-score   support

    negative       0.91      0.84      0.87      1044
    positive       0.91      0.96      0.93      1836

   micro avg       0.91      0.91      0.91      2880
   macro avg       0.91      0.90      0.90      2880
weighted avg       0.91      0.91      0.91      2880

Great news, our model "best_classifier_2" it is generalizing well over data it has never seen before. Let's see if the same applies for "best_classifier_1":

x_data = pd.read_csv('../csv/Hotels and travel dtm.csv', index_col=0)
y_data = pd.read_csv('../csv/Hotels and travel (classified).csv', index_col=0)
y_data = y_data['class']

X_train, X_test_val, y_train, y_test_val = train_test_split(x_data, y_data,  test_size=0.3, random_state=1)
X_test, X_val, y_test, y_val = train_test_split(X_test_val, y_test_val,  test_size=0.3, random_state=1)

#fit best classifier with the whole training set (HOTELS AND TRAVEL)
best_classifier_1.fit(X_train, y_train)
dump(best_classifier_1, "../models/Naive_model_ht.joblib")

#produce some predictions using the other category as input
x_data = pd.read_csv('../csv/Health and medical dtm.csv', index_col=0)
y_data = pd.read_csv('../csv/Health and medical (classified).csv', index_col=0)
y_data = y_data['class']

y_pred = best_classifier_1.predict(x_data)

#encode the predictions
le = preprocessing.LabelEncoder()
le.fit(['positive', 'negative'])
y_test_ = le.transform(y_data)
y_pred_ = le.transform(y_pred)

precision, recall, thresholds = precision_recall_curve(y_test_, y_pred_)
f1 = f1_score(y_test_, y_pred_ )

# calculate precision-recall AUC
auc_ = auc(recall, precision)

# calculate average precision score
ap = average_precision_score(y_test_, y_pred_, pos_label=1)
print('f1=%.3f auc=%.3f ap=%.3f' % (f1, auc_, ap))
    
plt.figure() 
lw = 2
fig = plt.gcf()
fig.set_size_inches(12, 10)
plt.plot(recall, precision, color='darkorange',
         lw=lw, label='AUC (area = %0.2f)' % auc_)
#plt.plot([0, 1], [0, 1], color='navy', lw=lw, linestyle='--')
plt.xlim([0.0, 1.0])
plt.ylim([0.0, 1.05])
plt.xlabel('Recall')
plt.ylabel('Precision')
plt.title('ROC HEALTH AND MEDICAL (with a model trained over HOTELS AND TRAVEL)', fontsize=20)
plt.legend(loc="lower right")
f1=0.973 auc=0.978 ap=0.957





<matplotlib.legend.Legend at 0x232854acfd0>

png

print(classification_report(y_data, y_pred))
              precision    recall  f1-score   support

    negative       0.96      0.89      0.93       407
    positive       0.96      0.99      0.97      1043

   micro avg       0.96      0.96      0.96      1450
   macro avg       0.96      0.94      0.95      1450
weighted avg       0.96      0.96      0.96      1450

Even better results, definetly this is due the amount of data, as the Hotels and Travel category contains twice more samples than the Health and Medical category. I would recommend then to deploy the model trained over Hotel and Travel.

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Scrapping Yelp reviews in the web. Transforming the data into a numeric representation and training a classifier to predict if a comment is positive or negative.

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