title: on a numpy 2D array - how to set last N array elements in each row to zero when N changes over rows
body: <p>Say, I have a 2D numpy array consists of 20 elements, for example:</p>
  
  <pre><code>arr = np.array([[1, 2, 15, 7],[9, 11, 17, 19],[5, 7, 5, 8],[19, 4, 1, 45],[10, 7, 14, 8]])
  </code></pre>
  
  <p>and an additional array:</p>
  
  <pre><code>to_zero = np.array([0, 2, 1, 3, 2])
  </code></pre>
  
  <p>now, for each row <code>i</code> I would like to make the last <code>to_zero[i]</code> elements equal to zero, so eventually we will get the following result:</p>
  
  <pre><code>res = np.array([[1, 2, 15, 7],[9, 11, 0, 0],[5, 7, 5, 0],[19, 0, 0, 0],[10, 7, 0, 0]])
  </code></pre>
  
  <p>I would like to do this operation on a very big array. 
  Is there any way to do this operation vectorized, with no loops, and no auxiliary arrays?</p>