def test_02_from_dataset_02(self):
"""Verify that a classifier can be constructed with initial weights for a fiven dataset."""
expected_weights = {'highly': 0, 'boring': 0, 'green': 0, 'eggs': 0}
classifier = PerceptronClassifier.from_dataset(
self.small_dataset_train_2)
if classifier is None:
self.fail(
msg=
'Constructing classifier for dataset failed: from_dataset returned None'
)
self.assertEqual(classifier.weights, expected_weights)
def nltk_movie_review_accuracy(num_iterations):
""" Try different number of features, and optimize number of training iterations."""
return 0, 0 # TODO: Exercise 4: remove line
(training_documents, dev_documents, test_documents) = load_reviews()
best_development_accuracy = 0.0
best_num_features = 0
best_classifier = None
best_feature_set = None
# Test different numbers of features.
for n in [100, 1000, 10000]:
print("Training with %d features..." % n)
# Training set
training_set = Dataset.from_document_collection(training_documents,
num_features=n)
# Development set
development_set = Dataset.from_document_collection(
dev_documents, feature_set=training_set.feature_set)
# Train classifier
classifier = PerceptronClassifier.from_dataset(training_set)
pass # TODO: Exercise 4: train the classifier
# Accuracies of classifier with n features
train_accuracy = classifier.test_accuracy(training_set)
development_accuracy = classifier.test_accuracy(development_set)
if development_accuracy > best_development_accuracy:
best_development_accuracy = development_accuracy
best_num_features = n
best_classifier = classifier.copy()
best_feature_set = training_set.feature_set
print(
"Best classifier with %d features: \t Train Accuracy: %.4f \t Dev Accuracy: %.4f"
% (n, train_accuracy, best_development_accuracy))
print("Best number of features: %d " % best_num_features)
print("Top features for positive class:")
print(best_classifier.features_for_class(True))
print("Top features for negative class:")
print(best_classifier.features_for_class(False))
# Compute test score for best setting.
testing_set = Dataset.from_document_collection(
test_documents, feature_set=best_feature_set)
testing_accuracy = best_classifier.test_accuracy(testing_set)
print("Test score for best setting: %.4f" % testing_accuracy)
return best_development_accuracy, testing_accuracy
