title: Formatting thousand separator for integers in a pandas dataframe
body: <p>I'm trying to use <code>'{:,}'.format(number)</code> like the example below to format a number in a pandas dataframe:</p>
  
  <pre><code># This works for floats and integers
  print '{:,}'.format(20000)
  # 20,000
  print '{:,}'.format(20000.0)
  # 20,000.0
  </code></pre>
  
  <p>The problem is that with a dataframe that has integers does not work, and in a dataframe with float works ok. See the examples:</p>
  
  <pre><code># Does not work. The format stays the same, does not show thousands separator
  df_int = DataFrame({"A": [20000, 10000]})
  print df_int.to_html(float_format=lambda x: '{:,}'.format(x))
  
  # Example of result
  # &lt;tr&gt;
  #   &lt;th&gt;0&lt;/th&gt;
  #   &lt;td&gt; 20000&lt;/td&gt;
  # &lt;/tr
  
  # Works OK
  df_float = DataFrame({"A": [20000.0, 10000.0]})
  print df_float.to_html(float_format=lambda x: '{:,}'.format(x))
  
  # Example of result
  # &lt;tr&gt;
  #   &lt;th&gt;0&lt;/th&gt;
  #   &lt;td&gt;20,000.0&lt;/td&gt;
  # &lt;/tr&gt;
  </code></pre>
  
  <p>What i'm doing wrong?</p>