title: Use numpy.argwhere to obtain the matching values in an np.array
body: <p>I'd like to use <code>np.argwhere()</code> to obtain the values in an <code>np.array</code>.</p>
  
  <p>For example:</p>
  
  <pre><code>z = np.arange(9).reshape(3,3)
  
  [[0 1 2]
   [3 4 5]
   [6 7 8]]
  
  zi = np.argwhere(z % 3 == 0)
  
  [[0 0]
   [1 0]
   [2 0]]
  </code></pre>
  
  <p>I want this array: <code>[0, 3, 6]</code> and did this:</p>
  
  <p><code>t = [z[tuple(i)] for i in zi] # -&gt; [0, 3, 6]</code></p>
  
  <p>I assume there is an easier way. </p>