title: Align numpy array according to another array
body: <p>I have a numpy array <code>a</code> containing arbitrary integer numbers, and I have another array <code>b</code>, (it is always a subset of  <code>a</code>, but the order of numbers in <code>b</code> is different than <code>a</code>.  I want to align the elements of <code>b</code> in the order it appears in <code>a</code>.</p>
  
  <pre><code>a = np.array([4,2,6,5,8,7,10,12]);
  b = np.array([10,6,2,12]),
  </code></pre>
  
  <p>I want <code>b</code> to be align as [2,6,10,12].  How can I do it in numpy efficiently ?</p>