title: Formatting thousand separator for numbers in a pandas dataframe
body: <p>I am trying to write a dataframe to a csv and I would like the .csv to be formatted with commas. I don't see any way on the to_csv docs to use a format or anything like this.</p>
  
  <p>Does anyone know a good way to be able to format my output?</p>
  
  <p>My csv output looks like this:</p>
  
  <pre><code>12172083.89 1341.4078   -9568703.592    10323.7222
  21661725.86 -1770.2725  12669066.38 14669.7118
  </code></pre>
  
  <p>I would like it to look like this:</p>
  
  <pre><code>12,172,083.89   1,341.4078  -9,568,703.592  10,323.7222
  21,661,725.86   -1,770.2725 12,669,066.38   14,669.7118
  </code></pre>