title: How to sort a dataframe by row names?
body: <p>I have a dataframe </p>
  
  <pre><code>  a b c d
  b 0 0 0 1
  d 1 0 0 1
  c 1 0 0 0
  a 2 0 0 1
  </code></pre>
  
  <p>How to sort the df by row names like </p>
  
  <pre><code>  a b c d
  a 2 0 0 1
  b 0 0 0 1
  c 1 0 0 0
  d 1 0 0 1
  </code></pre>