title: Dropping some columns when using to_csv in pandas
body: <p>I have a data frame which I want to write to tow files, one that contains all of the columns and one that has only a subset of the columns 
  So for this data frame: </p>
  
  <pre><code> Out_data
   Out[9]: 
      A     B                 C          D       E         F
  0  354   49985400          10          07   7.140899  0.212044
  1  738   49985400          10          07   7.140899  0.212044
  2  738   49985277          11          09   4.024423  0.098387
  3  246   49985279          10          07   7.140899  0.212044
  </code></pre>
  
  <p>I want to have it exported to two csv files, one that has all the data, and the second one that has only data from columns A,B, C and D, so that the csv would look like this: </p>
  
  <pre><code>  A,B,C,D,E,F
  354,49985400,10,07,7.140899,0.212044
  738,49985400,10,07,7.140899,0.212044
  738,49985277,11,09,4.024423,0.098387
  246,49985279,10,07,7.140899,0.212044
  </code></pre>
  
  <p>And the second one will look like: </p>
  
  <pre><code>  A,B,C,D
  354,49985400,10,07
  738,49985400,10,07
  738,49985277,11,09
  246,49985279,10,07
  </code></pre>
  
  <p>I am able to get the first file using: </p>
  
  <pre><code>Out_data.to_csv(filename, mode = 'w', index=False)
  </code></pre>
  
  <p>I tried using </p>
  
  <pre><code>Out_data.to_csv(filename, mode = 'w', cols = ['A','B','C','D'] ,index=False)
  </code></pre>
  
  <p>But I still go the exact same output file? 
  How can I get to_csv to export but drop some of the columns? </p>