title: Doing the opposite of pivot in pandas Python
body: <p>I'm trying to do the opposite of pivot in pandas. Wondering whether someone can provide some assistance? Trying to transform the data from the below</p>
  
  <pre><code>|Date|A|B|C|D|E |
  |----|-|-|-|-|--|
  |2005|1|2|3|4|50|
  |2006|6|7|8|9|10|
  </code></pre>
  
  <p>to </p>
  
  <pre><code>|Date|X|Val|
  |----|-|---|
  |2005|A|1  |
  |2005|B|2  |
  |2005|C|3  |
  etc 
  |2006|A|6  |
  etc
  |2006|E|10 |
  </code></pre>
  
  <p>Thank you very much</p>