title: Nested dictionary to pandas DataFrame
body: <p>My data looks like this:</p>
  
  <pre><code>{ outer_key1 : [ {key1: some_value},
                  {key2: some_value},
                  {key3: some_value} ],
    outer_key2 : [ {key1: some_value},
                  {key2: some_value},
                  {key3: some_value} ] }
  </code></pre>
  
  <p>The inner arrays are always the same lengths. key1, key2, key3 are also always the same.</p>
  
  <p>I want to convert this to a pandas DataFrame, where outer_key1, outer_key2, ... are the index and key1, key2, key3 are the columns.</p>
  
  <p>Edit:</p>
  
  <p>There's an issue in the data, which I believe is the reason the given solutions are not working. In a few cases, in the inner array there are three <code>None</code>s instead of the three dictionaries. Like this:</p>
  
  <p><code>outer_key3: [ None, None, None ]</code></p>