title: pandas DataFrame pivot table sum function not correct
body: <p>As the title mentions,</p>
  
  <pre><code>diag_code = df.pivot_table('PayabletoProvider',rows='DiagnosisCode',aggfunc=sum)
  </code></pre>
  
  <p>After applying the pivot function to my df, I am returned with data that dont make sense:</p>
  
  <p>DiagnosisCode ------    PayabletoProvider </p>
  
  <p>002    --------------------           NaN</p>
  
  <p>003    --------------------           NaN</p>
  
  <p>004    --------------------           1824.70143.80220.001640.2540.00282.00946.31250...</p>
  
  <p>005    --------------------           NaN</p>
  
  <p>006    --------------------           3324.95432.482400.65</p>
  
  <p>Dont understand why this happens, as results in Excel seem to be ok and sum accordingly.</p>
  
  <p>Would appreciate if somebody can help me fix this problem.</p>