title: Identifying the most useful words in differentiating between classes
body: <p>Is it possible to use tfidf (tfidfvectorizer in Python) to figure out which words are most important when trying to distinguish <em>between</em> two text classes (i.e., positive or negative sentiment, etc.)? For example, which words were most important for identifying the positive class, and then separately, which were most useful for identifying the negative class?</p>