title: Sort dataframe by first column, Pandas
body: <p>I have a dataframe with one column, which I would like to sort. 
  Typing following code gives me a sorted dataframe:</p>
  
  <pre><code>sort = tst.sort(["Mean"], ascending = False)
  
                  Mean
  SIMULATION          
  Sim_758     1.351917
  Sim_215     1.072942
  Sim_830     0.921284
  Sim_295     0.870272
  Sim_213     0.845990
  Sim_440     0.822394
  </code></pre>
  
  <p>This will be part of a function, which will be applied to other dataframes. For this reason I need to sort the dataframe without mentioning the column name "mean". </p>
  
  <p>Is there a way to sort a dataframe by the values of a column, only indicating the position of the column?</p>