title: how to group a list of dictionaries to get a list of their corresponding indices?
body: <p>Have a list of dictionaries, something like this:</p>
  <pre><code>l = [{'a':25}, {'a':25}, {'b':30}, {'c':200}, {'b':30}]  
  </code></pre>
  <p>want to find the distinct elements and their corresponding indices, something like this:</p>
  <pre><code>[
  ({'a':25}, [0,1]),
  ({'b':30}, [2,4]),
  ({'c':200}, [3]),
  ]
  </code></pre>
  <p>tried with itertools.groupby, but couldn't make it happen, perhaps I'm missing something, any other directions are great too.</p>