title: returning the element in one list based on the index and maximum value of an element in another list
body: <p>I have a list of lists which I converted into a numpy array:</p>
  
  <pre><code>lsts = ([[1,2,3], ['a','b','a']],
          [[4,5,6,7], ['a','a','b','b']], 
          [[1,2,3],['b','a','b']])
  
  np_lsts = np.array(lsts)
  </code></pre>
  
  <p>I want to return the largest element in the first list where a 'b' occurs in the second list. I think I have to use indexes but am stuck!</p>
  
  <p>i.e. I want to return (2, 7, 3) in this case</p>