title: Most efficient way of iterating over a numpy array by axis?
body: <p>I have a numpy array with 3 dimensions. 
  I want to iterate over 2 dims and pull everything out in the 3rd dim. 
  I.E:</p>
  
  <pre><code>arr = numpy.random.rand(3,5,5)
  
  for i in range(arr.shape[1]):
      for j in range(arr.shape[2]):
          print arr[:, i, j]
  </code></pre>
  
  <p>Is this the most efficient way to loop? I know numpy provides the more efficient <code>nditer</code> function for looping, but it doesn't seem like it is able to do stuff like this</p>
  
  <p>The actual arrays I'll be using will have a size of about 30x256x256</p>