title: Initialize a dataframe without a header
body: <p>To create a pandas dataframe with a header I can do:</p>
  
  <pre><code>df = pd.DataFrame({'a':[1,2,3], 'b':[4,5,6]})
  
     a  b
  0  1  4
  1  2  5
  2  3  6
  </code></pre>
  
  <p>How would I create one without a header, something like:</p>
  
  <pre><code>df = pd.DataFrame([[1,2,3],[4,5,6]])
  
     0  1  2
  0  1  2  3
  1  4  5  6
  # seems to create three headers, '0', '1', and '2' for the index of the array.
  </code></pre>