title: ValueError: setting an array element with a sequence while training KD TRee on TFIDF
body: <p>I am trying to train a KD-Tree on TF-IDF of a document corpus but it gives </p>
  
  <pre><code>ValueError: setting an array element with a sequence.
  </code></pre>
  
  <p>The code and the error description are below. Can someone help me figure out the problem?</p>
  
  <p>Code:</p>
  
  <pre><code>t0 = time.time()
  count_vect = CountVectorizer()
  X_train_counts = count_vect.fit_transform(X)
  
  tfidf_transformer = TfidfTransformer()
  X_train_tfidf = tfidf_transformer.fit_transform(X_train_counts)
  
  t1 = time.time()
  total = t1-t0
  print "TF-IDF built:", total
  
  #######################------------------------############################
  
  t0 = time.time()
  #nbrs = NearestNeighbors(n_neighbors=20, algorithm='kd_tree', metric='euclidean')
  #nbrs.fit(X_train_tfidf)#,Y)
  nbrs = KDTree(np.array(X_train_tfidf), leaf_size=100) 
  
  
  t1 = time.time()
  total = t1-t0
  print "KNN Trained:", total
  
  #######################------------------------############################
  </code></pre>
  
  <p>This is the error:</p>
  
  <pre><code>TF-IDF built: 0.108999967575
  Traceback (most recent call last):
    File ".\tfidf_knn.py", line 48, in &lt;module&gt;
      nbrs = KDTree(np.array(X_train_tfidf), leaf_size=100)
    File "sklearn/neighbors/binary_tree.pxi", line 1055, in sklearn.neighbors.kd_tree.BinaryTree.__init__ (sklearn\neighbo
  rs\kd_tree.c:8298)
    File "C:\Anaconda2\lib\site-packages\numpy\core\numeric.py", line 474, in asarray
      return array(a, dtype, copy=False, order=order)
  ValueError: setting an array element with a sequence.
  </code></pre>