title: write a dictionary of dictionaries (with unknown size) as a matrix
body: <p>I have a python dictionary, for example:</p>
  
  <pre><code> my_dict = {100: {0.5: 1, 0.6: 0}, 200: {0.5: 1, 0.6: 1}}
  </code></pre>
  
  <p>i.e., the it is a dictionary of dictionaries.</p>
  
  <p>I would like to print it as a matrix, like this:</p>
  
  <pre><code>     0.5, 0.6
  100  1    0
  200  1    1
  </code></pre>
  
  <p>I wanted to use something like this:
  <a href="https://stackoverflow.com/questions/17330139/python-printing-a-dictionary-as-a-horizontal-table-with-headers">Python - Printing a dictionary as a horizontal table with headers</a></p>
  
  <p>but the problem is that I don't know the size of either the dictionary (how many keys it has), or the sub-dictionary... </p>