Classification of text documents using sparse featuresΒΆ
This is an example showing how the scikit-learn can be used to classify documents by topics using a bag-of-words approach. This example uses a scipy.sparse matrix to store the features instead of standard numpy arrays.
The dataset used in this example is the 20 newsgroups dataset which will be automatically downloaded and then cached.
You can adjust the number of categories by giving there name to the dataset loader or setting them to None to get the 20 of them.
This example demos various linear classifiers with different training strategies.
To run this example use:
% python examples/document_classification_20newsgroups.py [options]
Options are:
--report Print a detailed classification report. --confusion-matrix Print the confusion matrix.
Python source code: document_classification_20newsgroups.py
print __doc__
# Author: Peter Prettenhofer <peter.prettenhofer@gmail.com>
# Olivier Grisel <olivier.grisel@ensta.org>
# Mathieu Blondel <mathieu@mblondel.org>
# License: Simplified BSD
from time import time
import logging
import os
import sys
from scikits.learn.datasets import fetch_20newsgroups
from scikits.learn.feature_extraction.text import Vectorizer
from scikits.learn.linear_model import RidgeClassifier
from scikits.learn.svm.sparse import LinearSVC
from scikits.learn.linear_model.sparse import SGDClassifier
from scikits.learn import metrics
# Display progress logs on stdout
logging.basicConfig(level=logging.INFO,
format='%(asctime)s %(levelname)s %(message)s')
# parse commandline arguments
argv = sys.argv[1:]
if "--report" in argv:
print_report = True
else:
print_report = False
if "--confusion-matrix" in argv:
print_cm = True
else:
print_cm = False
################################################################################
# Load some categories from the training set
categories = [
'alt.atheism',
'talk.religion.misc',
'comp.graphics',
'sci.space',
]
# Uncomment the following to do the analysis on all the categories
#categories = None
print "Loading 20 newsgroups dataset for categories:"
print categories
data_train = fetch_20newsgroups(subset='train', categories=categories,
shuffle=True, random_state=42)
data_test = fetch_20newsgroups(subset='test', categories=categories,
shuffle=True, random_state=42)
print "%d documents (training set)" % len(data_train.filenames)
print "%d documents (testing set)" % len(data_test.filenames)
print "%d categories" % len(data_train.target_names)
print
# split a training set and a test set
filenames_train, filenames_test = data_train.filenames, data_test.filenames
y_train, y_test = data_train.target, data_test.target
print "Extracting features from the training dataset using a sparse vectorizer"
t0 = time()
vectorizer = Vectorizer()
X_train = vectorizer.fit_transform((open(f).read() for f in filenames_train))
print "done in %fs" % (time() - t0)
print "n_samples: %d, n_features: %d" % X_train.shape
print
print "Extracting features from the test dataset using the same vectorizer"
t0 = time()
X_test = vectorizer.transform((open(f).read() for f in filenames_test))
print "done in %fs" % (time() - t0)
print "n_samples: %d, n_features: %d" % X_test.shape
print
################################################################################
# Benchmark classifiers
def benchmark(clf):
print 80 * '_'
print "Training: "
print clf
t0 = time()
clf.fit(X_train, y_train)
train_time = time() - t0
print "train time: %0.3fs" % train_time
t0 = time()
pred = clf.predict(X_test)
test_time = time() - t0
print "test time: %0.3fs" % test_time
score = metrics.f1_score(y_test, pred)
print "f1-score: %0.3f" % score
nnz = clf.coef_.nonzero()[0].shape[0]
print "non-zero coef: %d" % nnz
print
if print_report:
print "classification report:"
print metrics.classification_report(y_test, pred,
target_names=categories)
if print_cm:
print "confusion matrix:"
print metrics.confusion_matrix(y_test, pred)
print
return score, train_time, test_time
for clf, name in ((RidgeClassifier(), "Ridge Classifier"),):
print 80*'='
print name
results = benchmark(clf)
for penalty in ["l2", "l1"]:
print 80 * '='
print "%s penalty" % penalty.upper()
# Train Liblinear model
liblinear_results = benchmark(LinearSVC(loss='l2', penalty=penalty, C=1000,
dual=False, tol=1e-3))
# Train SGD model
sgd_results = benchmark(SGDClassifier(alpha=.0001, n_iter=50,
penalty=penalty))
# Train SGD with Elastic Net penalty
print 80 * '='
print "Elastic-Net penalty"
sgd_results = benchmark(SGDClassifier(alpha=.0001, n_iter=50,
penalty="elasticnet"))