title: TypeError with accessing to coo_matrix by index
body: <p>I have coo_matrix <code>X</code> and indexes <code>trn_idx</code> by which I would like to get access of that maxtrix</p>
  
  <pre><code>print (type(X  ), X.shape)
  print (type(trn_idx), trn_idx.shape)
  
  &lt;class 'scipy.sparse.coo.coo_matrix'&gt; (1503424, 2795253)
  &lt;class 'numpy.ndarray'&gt; (1202739,)
  </code></pre>
  
  <p>Calling this way:</p>
  
  <pre><code>X[trn_idx]
  TypeError: only integer scalar arrays can be converted to a scalar index
  </code></pre>
  
  <p>Either this way:</p>
  
  <pre><code> X[trn_idx.astype(int)] #same error
  </code></pre>
  
  <p>How to access by index?</p>