title: Pandas: TypeError: sort_values() missing 1 required positional argument: 'by'
body: <p>I am facing TypeError: sort_values() missing 1 required positional argument: 'by'</p>
  
  <pre><code>for i in range(0,len(data_sims.index)):
  for j in range(1,len(data_sims.columns)):
      user = data_sims.index[i]
      serial = data_sims.columns[j]
  
      if dataUser.ix[i][j] == 1:
          data_sims.ix[i][j] = 0
      else:
          serial_top_names = data_neighbours.ix[serial][1:10]
          serial_top_sims = dataSim.ix[serial].sort_values(ascending=False)[1:10]
          user_preferences = dataUser.ix[user,serial_top_names]
  
          data_sims.ix[i][j] = getScore(user_preferences,serial_top_sims)
  </code></pre>
  
  <p>Detailed Error:</p>
  
  <pre>
  > ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
   in ()
        9         else:
       10             serial_top_names = data_neighbours.ix[serial][1:10]
  ---> 11             serial_top_sims = dataSim.ix[serial].sort_values(ascending=False)[1:10]
       12             user_preferences = dataUser.ix[user,serial_top_names]
       13 
  
  TypeError: sort_values() missing 1 required positional argument: 'by'
  </pre>
  
  <p>I tried using following but didn't work</p>
  
  <pre><code>pd.DataFrame.sort_values(dataSim,ascending=[0])[1:10]
  </code></pre>
  
  <p>Is there anything that I'm missing?</p>