title: Groupby column suffix in pandas
body: <p>Given a dataframe:</p>
  
  <pre><code>     val1_aa  val1_bb  val2_aa  val2_bb  val2_cc  val3_cc
  id                                                       
  100        6        0        3        4        3        1
  200        0        1        0        0        1        0
  300        5        1        1        0        4        0
  400        0        3        1        5        7        1
  </code></pre>
  
  <p>I'd like to sum all columns in order of the suffix in each column header. My desired output:</p>
  
  <pre><code>     aa  bb  cc
  id             
  100   9   4   4
  200   0   1   1
  300   6   1   4
  400   1   8   8
  </code></pre>
  
  <p>How do I get this? </p>
  
  <hr>
  
  <p><sub>Answer posted below.</sub></p>