title: Python: Sort nested dictionary by value
body: <p>I am working with a large dictionary (500+ keys) that has as its values 2 dictionaries (that have as their values numerics) and two lists (one of numerics with length=~10, one of bools with length=~50).  I would like to get some sort of representation, be it a list or tuple, that sorts the original dictionary by one of the numeric values inside of one of the inner dictionaries.  Is there a way to do this?  </p>
  
  <p>For reference, here is a single entry for key 'WHR' from the (large) dictionary I am working with: </p>
  
  <pre><code>dd_rf['WHR'] = {'counts': {'num': 81.0,
    'numClassCorrect': 64,
    'numClassDown': 20,
    'numClassDownCorrect': 20,
    'numClassIncorrect': 17.0,
    'numClassUp': 61,
    'numClassUpCorrect': 44,
    'numDown': 37,
    'numUp': 44},
   'imp': array([ 0.50924113,  0.06348138,  0.07851569,  0.03005051,  0.04103215,
          0.05646218,  0.03682958,  0.03642228,  0.04282599,  0.01439416,
          0.03090185,  0.0598431 ]),
   'rates': {'correctDownRate': 1.0,
    'correctRate': 0.7901234567901234,
    'correctUpRate': 0.7213114754098361,
    'downRate': 0.4567901234567901,
    'upRate': 0.5432098765432098},
   'results': array([False, False,  True,  True,  True,  True, False, False,  True,
         False,  True,  True, False, False,  True, False,  True,  True,
          True,  True,  True,  True,  True,  True,  True, False, False,
          True,  True,  True,  True,  True,  True,  True,  True,  True,
          True, False,  True, False, False,  True,  True,  True,  True,
          True,  True,  True,  True, False,  True, False,  True,  True,
          True,  True,  True, False, False, False,  True,  True,  True,
          True,  True,  True,  True,  True,  True,  True, False,  True,
          True,  True, False,  True,  True,  True,  True,  True,  True], dtype=bool)}
  </code></pre>
  
  <p>So, in the context of my work, I would like to sort the entire dictionary 'dd_rf' by the values of 'dd_rf[key]['rates']['correctRate'] in descending order.  The value corresponding to the given sort criteria in the above example is 'correctRate': 0.7901234567901234.  </p>
  
  <p>Thanks!  Please let me know if I can provide any more background information.</p>