title: Combine duplicated columns within a DataFrame
body: <p>If I have a dataframe that has columns that include the same name, is there a way to combine the columns that have the same name with some sort of function (i.e. sum)?</p>
  
  <p>For instance with:</p>
  
  <pre><code>In [186]:
  
  df["NY-WEB01"].head()
  Out[186]:
                  NY-WEB01    NY-WEB01
  DateTime        
  2012-10-18 16:00:00  5.6     2.8
  2012-10-18 17:00:00  18.6    12.0
  2012-10-18 18:00:00  18.4    12.0
  2012-10-18 19:00:00  18.2    12.0
  2012-10-18 20:00:00  19.2    12.0
  </code></pre>
  
  <p>How might I collapse the NY-WEB01 columns (there are a  bunch of duplicate columns, not just NY-WEB01) by summing each row where the column name is the same?</p>