I am trying to train a model on text classification. I have a large labeled dataset. Documents are set of comments, notes on a incident. Labels are high level categories for the incidents. As expected, the comments and notes are subjected to human errors, misspellings.

What should be the features for this classification? I have tried TfIdfVectorizer, with tokenizer which uses PorterStemmer. Also i am including ngrams of size 1-4 as features. What additional features can be defined for such a data set?

   df = read_csv(filename, sep="|", na_values=[" "]).fillna(" ")
   le = preprocessing.LabelEncoder()
   target = le.fit_transform(df['label'])

   vectorizer = TfidfVectorizer(sublinear_tf=True, 

   train = vectorizer.fit_transform(df['data'])
   X_train, X_test, y_train , y_test = cross_validation.train_test_split(train, target, test_size=5000, random_state=0)
   clf = MultinomialNB(alpha=.1)
   clf.fit(X_train, y_train)
   pred = clf.predict(X_test)

My dataset contains about 300k documents, and vectorizer can produce upto 50k features. I have even tried chisquare to reduce the number of features to 5k, but still accuracy does not improve much. The accuracy was 42% when the data set is 10k or so. The accuracy starts going bad as the data size grows.

Classifiers Tried

SGDClassifier Perceptron PassiveAggressiveClassifier BernoulliNB, MultinomialNB KNeighborsClassifier NearestCentroid RandomForestClassifier

  • 1
    $\begingroup$ "The accuracy starts going bad as the data size grows." The annotation of your training data might be noisy. $\endgroup$ Nov 1, 2015 at 7:05
  • $\begingroup$ @xeon: indeed it is a sign of overfitting. $\endgroup$
    – Michael M
    Nov 1, 2015 at 8:33
  • $\begingroup$ sorry how to proceed in this kind of problem? $\endgroup$ Nov 2, 2015 at 4:31
  • $\begingroup$ whay you don't try bayesian networks, they do text classifications very well. $\endgroup$
    – pmargreff
    Sep 24, 2016 at 9:47

1 Answer 1


If you have not done so yet I would suggest to test


and play with the parameters with a grid search

 parameters={'alpha': [1e-2,1e-3,1e-4,1e-5,1e-6,1e-7],'n_iter':[10,20,30,100,200,300] }

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