title: Splitting multiple columns into rows in pandas dataframe
body: <p>I have a pandas dataframe as follows:</p>
  
  <pre><code>ticker    account      value         date
  aa       assets       100,200       20121231, 20131231
  bb       liabilities  50, 150       20141231, 20131231
  </code></pre>
  
  <p>I would like to split <code>df['value']</code> and <code>df['date']</code> so that the dataframe looks like this:</p>
  
  <pre><code>ticker    account      value         date
  aa       assets       100           20121231
  aa       assets       200           20131231 
  bb       liabilities  50            20141231
  bb       liabilities  150           20131231
  </code></pre>
  
  <p>Would greatly appreciate any help. </p>