title: How to convert a scipy csr_matrix back into lists of row, col and data?
body: <p>I have a scipy csr_matrix that was created this way as specified in the documentation:</p>
  
  <pre><code>import numpy as np
  from scipy.sparse import csr_matrix
  row = np.array([0, 0, 1, 2, 2, 2])
  col = np.array([0, 2, 2, 0, 1, 2])
  data = np.array([1, 2, 3, 4, 5, 6])
  mtr = csr_matrix((data, (row, col)))
  mtr.toarray()
  array([[1, 0, 2],
         [0, 0, 3],
         [4, 5, 6]])
  </code></pre>
  
  <p>How do I efficiently convert such a matrix <code>mtr</code> back into the initial three lists <code>row</code>, <code>col</code> and <code>data</code>?</p>