title: IndexError : index out of bounds
body: <p>I have implemented MultinomialNB but I get this message. Please help me to solve it. Here my code : </p>
  
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  <pre class="snippet-code-html lang-html prettyprint-override"><code>kf = KFold(len(X), n_folds=2, shuffle=True, random_state=9999)
  model_train_index = []
  model_test_index = []
  model = 0
  
  for k, (index_train, index_test) in enumerate(kf):
      X_train, X_test, y_train, y_test = X.ix[index_train,:], X.ix[index_test,:],y[index_train], y[index_test]
      clf = MultinomialNB(alpha=0.1).fit(X_train, y_train)
      score = clf.score(X_test, y_test)
      f1score = f1_score(y_test, clf.predict(X_test))
      precision = precision_score(y_test, clf.predict(X_test))
      recall = recall_score(y_test, clf.predict(X_test))
      print('Model %d has accuracy %f with | f1score: %f | precision: %f | recall : %f'%(k,score, f1score, precision, recall))
      model_train_index.append(index_train)
      model_test_index.append(index_test)
      model+=1</code></pre>
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  <p>and then I get result like this : </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-html lang-html prettyprint-override"><code>IndexError                                Traceback (most recent call last)
  &lt;ipython-input-3-df0b24edb687&gt; in &lt;module&gt;()
        5 
        6 for k, (index_train, index_test) in enumerate(kf):
  ----&gt; 7     X_train, X_test, y_train, y_test = X.ix[index_train,:], X.ix[index_test,:],y[index_train], y[index_test]
        8     clf = MultinomialNB(alpha=0.1).fit(X_train, y_train)
        9     score = clf.score(X_test, y_test)
  
  IndexError: index 100 is out of bounds for axis 0 with size 100</code></pre>
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