title: string and unequal feature vectors in sklearn
body: <p>i have string and unequal feature vectors . How do I use it in sklearn? Without conversion to binary</p>
  
  <pre><code>x=[["a","b"],["a","d","c"],["b","f"],["c","f","d"]]
  y=[1,0,1,0]
  from sklearn import ensemble
  clf = ensemble.RandomForestClassifier(n_estimators=100)
  clf.fit(x,y)
  xt=[["b","f","d"],["a","c"]]
  clflist=clf.predict(xt)
  print(clflist)
  </code></pre>