title: Pandas melt to get multiple variable and value columns
body: <p>I have a Pandas DataFrame</p>
  
  <pre><code>data = {
  "SomeCol":[1,2],
  "Group1":['x','y'],
  "Group2":['a','b'],
  "SomeAgg":[100,200]
  }
  df = pd.DataFrame(data)
  
     SomeCol Group1 Group2  SomeAgg
  0        1      x      a      100
  1        2      y      b      200
  </code></pre>
  
  <p>How can I get this:</p>
  
  <pre><code>   SomeCol    Var1    Var2 Var1_value Var2_value  SomeAgg
  0        1  Group1  Group2          x          a      100
  1        2  Group1  Group2          y          b      200
  </code></pre>
  
  <p>I have tried <code>pd.melt</code> function which gives only one variable and one value columns.</p>
  
  <p>Any help would be appreciated</p>