title: Create MultiIndex pandas DataFrame from dictionary with tuple keys
body: <p>I'd like to efficiently create a <strong>pandas DataFrame</strong> from a Python <strong>collections.Counter</strong> dictionary .. but there's an additional requirement.</p>
  
  <p>The <strong>Counter</strong> dictionary looks like this:</p>
  
  <pre><code>(a, b) : 5
  (c, d) : 7
  (a, d) : 2
  </code></pre>
  
  <p>Those dictionary keys are tuples where the first is to become the row, and the second the column of the dataframe.</p>
  
  <p>The resulting <strong>DataFrame</strong> should look like this:</p>
  
  <pre><code>   b  d
  a  5  2
  c  0  7
  </code></pre>
  
  <p>For larger data I don't want to create a dataframe using the growth method <code>df[a][b]= 5</code> etc as that is incredibly inefficient as it creates a copy of the new dataframe every time such an extension is done (I'm let to believe). </p>
  
  <p>Perhaps the right answer is to go via a <strong>numpy array</strong>?</p>