title: Aggregate items in dict
body: <p>I have a list like this:</p>
  
  <pre><code>A = [{u'CI': {u'RP': 1}}, {u'CI': {u'RP': 1}},  {u'JI': {u'RP': 1}}]
  </code></pre>
  
  <p>and I want merge same keys and increment value in dict.</p>
  
  <p>Example: </p>
  
  <p>From these values : </p>
  
  <pre><code>{u'CI': {u'RP': 1}}, {u'CI': {u'RP': 1}}
  </code></pre>
  
  <p>I will have: </p>
  
  <pre><code>{u'CI': {u'RP': 2}}
  </code></pre>
  
  <p>final list result is:</p>
  
  <pre><code>A = [{u'CI': {u'RP': 2}}, {u'JI': {u'RP': 1}]
  </code></pre>