title: pandas converting floats to strings without decimals
body: <p>I have a dataframe</p>
  
  <pre><code>df = pd.DataFrame([
          ['2', '3', 'nan'],
          ['0', '1', '4'],
          ['5', 'nan', '7']
      ])
  
  print df
  
     0    1    2
  0  2    3  nan
  1  0    1    4
  2  5  nan    7
  </code></pre>
  
  <p>I want to convert these strings to numbers and sum the columns and convert back to strings.</p>
  
  <p>Using <code>astype(float)</code> seems to get me to the number part.  Then summing is easy with <code>sum()</code>.  Then back to strings should be easy too with <code>astype(str)</code></p>
  
  <pre><code>df.astype(float).sum().astype(str)
  
  0     7.0
  1     4.0
  2    11.0
  dtype: object
  </code></pre>
  
  <p>That's almost what I wanted.  I wanted the string version of integers.  But floats have decimals.  How do I get rid of them?</p>
  
  <p>I want this</p>
  
  <pre><code>0     7
  1     4
  2    11
  dtype: object
  </code></pre>