title: What is the difference between TfidfVectorizer.fit_transfrom and tfidf.transform?
body: <p>In Tfidf.fit_transform we are only using the parameters X and have not used y for fitting the data set.
  Is this right?
  We are generating the tfidf matrix for only parameters of the training set.We are not using ytrain in fitting the model.
  Then how do we make predictions for the test data set</p>