title: Transpose only few columns and rows from a dataframe
body: <p>I am looking to transpose only certain columns in my dataframe and their values by keeping starting columns fixed.</p>
  
  <p>I/P frame:</p>
  
  <pre><code>Type    Class   24/01/2018  25/01/2018  26/01/2018
  Plant1  Plant   5498    5998    5815
  Plant2  Plant   3416    4844    4991
  Veg1    Vegetable   5426    5464    3756
  Veg2    Vegetable   5317    4616    7528
  </code></pre>
  
  <p>O/P frame:</p>
  
  <pre><code>Type    Class   Value   Date
  Plant1  Plant   5498    24/01/2018
  Plant1  Plant   5998    25/01/2018
  Plant1  Plant   5815    26/01/2018
  Veg1    Vegetable   5426    24/01/2018
  Veg1    Vegetable   5464    25/01/2018
  Veg1    Vegetable   3756    26/01/2018
  </code></pre>
  
  <p>I normally do this in excel, and tried using pivot in pandas but unable to get an idea to implement it. Can anyone help in giving me a lead?</p>
  
  <p>Thanks</p>