ch08.py

# Sebastian Raschka, 2015 (http://sebastianraschka.com)
# Python Machine Learning - Code Examples
#
# Chapter 8 - Applying Machine Learning To Sentiment Analysis
#
# S. Raschka. Python Machine Learning. Packt Publishing Ltd., 2015.
# GitHub Repo: https://github.com/rasbt/python-machine-learning-book
#
# License: MIT
# https://github.com/rasbt/python-machine-learning-book/blob/master/LICENSE.txt

import pyprind
import pandas as pd
import os
import numpy as np
import re
import nltk
from sklearn.feature_extraction.text import CountVectorizer
from sklearn.feature_extraction.text import TfidfTransformer
from sklearn.grid_search import GridSearchCV
from sklearn.pipeline import Pipeline
from sklearn.linear_model import LogisticRegression
from sklearn.feature_extraction.text import TfidfVectorizer
from sklearn.feature_extraction.text import HashingVectorizer
from sklearn.linear_model import SGDClassifier
from nltk.stem.porter import PorterStemmer
from nltk.corpus import stopwords


#############################################################################
print(50 * '=')
print('Section: Obtaining the IMDb movie review dataset')
print(50 * '-')

print('!! This script assumes that the movie dataset is located in the'
      ' current directory under ./aclImdb')

_ = input('Please hit enter to continue.')

basepath = './aclImdb'

"""
labels = {'pos': 1, 'neg': 0}
pbar = pyprind.ProgBar(50000)
df = pd.DataFrame()
for s in ('test', 'train'):
    for l in ('pos', 'neg'):
        path = os.path.join(basepath, s, l)
        for file in os.listdir(path):
            with open(os.path.join(path, file), 'r',
                      encoding='utf-8') as infile:
                txt = infile.read()
            df = df.append([[txt, labels[l]]], ignore_index=True)
            pbar.update()
df.columns = ['review', 'sentiment']


np.random.seed(0)
df = df.reindex(np.random.permutation(df.index))

df.to_csv('./movie_data.csv', index=False)
"""

df = pd.read_csv('../datasets/movie/movie_data.csv')
print('Excerpt of the movie dataset', df.head(3))


#############################################################################
print(50 * '=')
print('Section: Transforming documents into feature vectors')
print(50 * '-')

count = CountVectorizer()
docs = np.array(['The sun is shining',
                 'The weather is sweet',
                 'The sun is shining and the weather is sweet'])
bag = count.fit_transform(docs)

print('Vocabulary', count.vocabulary_)
print('bag.toarray()', bag.toarray())


#############################################################################
print(50 * '=')
print('Section: Assessing word relevancy via term frequency-inverse'
      ' document frequency')
print(50 * '-')

np.set_printoptions(precision=2)
tfidf = TfidfTransformer(use_idf=True, norm='l2', smooth_idf=True)
print(tfidf.fit_transform(count.fit_transform(docs)).toarray())

tf_is = 2
n_docs = 3
idf_is = np.log((n_docs + 1) / (3 + 1))
tfidf_is = tf_is * (idf_is + 1)
print('tf-idf of term "is" = %.2f' % tfidf_is)


tfidf = TfidfTransformer(use_idf=True, norm=None, smooth_idf=True)
raw_tfidf = tfidf.fit_transform(count.fit_transform(docs)).toarray()[-1]
print('raw tf-idf', raw_tfidf)

l2_tfidf = raw_tfidf / np.sqrt(np.sum(raw_tfidf**2))
l2_tfidf
print('l2 tf-idf', l2_tfidf)


#############################################################################
print(50 * '=')
print('Section: Cleaning text data')
print(50 * '-')

print('Excerpt:\n\n', df.loc[0, 'review'][-50:])


def preprocessor(text):
    text = re.sub('<[^>]*>', '', text)
    emoticons = re.findall('(?::|;|=)(?:-)?(?:\)|\(|D|P)', text)
    text = re.sub('[\W]+', ' ', text.lower()) +\
        ' '.join(emoticons).replace('-', '')
    return text

print('Preprocessor on Excerpt:\n\n', preprocessor(df.loc[0, 'review'][-50:]))

res = preprocessor("</a>This :) is :( a test :-)!")
print('Preprocessor on "</a>This :) is :( a test :-)!":\n\n', res)

df['review'] = df['review'].apply(preprocessor)


#############################################################################
print(50 * '=')
print('Section: Processing documents into tokens')
print(50 * '-')

porter = PorterStemmer()


def tokenizer(text):
    return text.split()


def tokenizer_porter(text):
    return [porter.stem(word) for word in text.split()]


t1 = tokenizer('runners like running and thus they run')
print("Tokenize: 'runners like running and thus they run'")
print(t1)

t2 = tokenizer_porter('runners like running and thus they run')
print("\nPorter-Tokenize: 'runners like running and thus they run'")
print(t2)

nltk.download('stopwords')


print('remove stop words')
stop = stopwords.words('english')

r = [w for w in tokenizer_porter('a runner likes running and runs a lot')[-10:]
     if w not in stop]

print(r)


#############################################################################
print(50 * '=')
print('Section: Training a logistic regression model'
      ' for document classification')
print(50 * '-')


X_train = df.loc[:25000, 'review'].values
y_train = df.loc[:25000, 'sentiment'].values
X_test = df.loc[25000:, 'review'].values
y_test = df.loc[25000:, 'sentiment'].values


tfidf = TfidfVectorizer(strip_accents=None,
                        lowercase=False,
                        preprocessor=None)

param_grid = [{'vect__ngram_range': [(1, 1)],
               'vect__stop_words': [stop, None],
               'vect__tokenizer': [tokenizer, tokenizer_porter],
               'clf__penalty': ['l1', 'l2'],
               'clf__C': [1.0, 10.0, 100.0]},
              {'vect__ngram_range': [(1, 1)],
               'vect__stop_words': [stop, None],
               'vect__tokenizer': [tokenizer, tokenizer_porter],
               'vect__use_idf':[False],
               'vect__norm':[None],
               'clf__penalty': ['l1', 'l2'],
               'clf__C': [1.0, 10.0, 100.0]},
              ]

lr_tfidf = Pipeline([('vect', tfidf),
                     ('clf', LogisticRegression(random_state=0))])

gs_lr_tfidf = GridSearchCV(lr_tfidf, param_grid,
                           scoring='accuracy',
                           cv=5,
                           verbose=1,
                           n_jobs=-1)

gs_lr_tfidf.fit(X_train, y_train)

print('Best parameter set: %s ' % gs_lr_tfidf.best_params_)
print('CV Accuracy: %.3f' % gs_lr_tfidf.best_score_)


clf = gs_lr_tfidf.best_estimator_
print('Test Accuracy: %.3f' % clf.score(X_test, y_test))


#############################################################################
print(50 * '=')
print('Section: Working with bigger data - online'
      ' algorithms and out-of-core learning')
print(50 * '-')

stop = stopwords.words('english')


def tokenizer(text):
    text = re.sub('<[^>]*>', '', text)
    emoticons = re.findall('(?::|;|=)(?:-)?(?:\)|\(|D|P)', text.lower())
    text = re.sub('[\W]+', ' ', text.lower()) +\
        ' '.join(emoticons).replace('-', '')
    tokenized = [w for w in text.split() if w not in stop]
    return tokenized


def stream_docs(path):
    with open(path, 'r', encoding='utf-8') as csv:
        next(csv)  # skip header
        for line in csv:
            text, label = line[:-3], int(line[-2])
            yield text, label

next(stream_docs(path='./movie_data.csv'))


def get_minibatch(doc_stream, size):
    docs, y = [], []
    try:
        for _ in range(size):
            text, label = next(doc_stream)
            docs.append(text)
            y.append(label)
    except StopIteration:
        return None, None
    return docs, y


vect = HashingVectorizer(decode_error='ignore',
                         n_features=2**21,
                         preprocessor=None,
                         tokenizer=tokenizer)

clf = SGDClassifier(loss='log', random_state=1, n_iter=1)
doc_stream = stream_docs(path='./movie_data.csv')

pbar = pyprind.ProgBar(45)

classes = np.array([0, 1])
for _ in range(45):
    X_train, y_train = get_minibatch(doc_stream, size=1000)
    if not X_train:
        break
    X_train = vect.transform(X_train)
    clf.partial_fit(X_train, y_train, classes=classes)
    pbar.update()


X_test, y_test = get_minibatch(doc_stream, size=5000)
X_test = vect.transform(X_test)
print('Accuracy: %.3f' % clf.score(X_test, y_test))

clf = clf.partial_fit(X_test, y_test)