title: CountVectorizer returns only zeros
body: <p>I am trying to extract some features from a given document, given a pre-defined set of features. </p>
  
  <pre><code>from sklearn.feature_extraction.text import CountVectorizer
  features = ['a', 'b', 'c']
  doc = ['a', 'c']
  
  vectoriser = CountVectorizer()
  vectoriser.vocabulary = features
  vectoriser.fit_transform(doc)
  </code></pre>
  
  <p>However the output, is a 2x3 array, filled in with zeros instead of :</p>
  
  <pre><code>desired_output = [[1, 0, 0]
                    [0, 0, 1]]
  </code></pre>
  
  <p>Any help would be much appreciated</p>