title: flatMap a Dictionary of Dictionaries in Swift
body: <p>I have an <code>NSEnumerator</code> which contains nested key value objects like this:</p>
  
  <pre><code> [ "posts" :
      ["randonRootKey1" :
          ["randomChildKey1" : [:] ]
      ], 
      ["randonRootKey2" :
          ["randomChildKey2" : [:] ],
          ["randomChildKey3" : [:] ],
      ]  
  ]
  
  - posts
  -- user1
  --- posts
  ----post
  -- user2
  -- posts
  --- post 
  </code></pre>
  
  <p>I want to extract all posts of all users in one array ... last child and all parents are dictionaries</p>
  
  <p>I want to flatMap it to be :</p>
  
  <pre><code>[
          ["randomChildKey1" : [:] ],
          ["randomChildKey2" : [:] ],
          ["randomChildKey3" : [:] ]
  ]
  </code></pre>
  
  <p>Note that I have extracted the objects of each root dictionary.</p>
  
  <p>I have tried :</p>
  
  <pre><code>let sub = snapshot.children.flatMap({$0}) 
  </code></pre>
  
  <p>but does not seem to work</p>