title: Reshape Dataframe from horizontal column to vertical
body: <p>Is there any efficient way to reshape a dataframe from:</p>
  
  <p>(A1, A2, A3, B1, B2, B3, C1, C2, C3, TT, YY and ZZ are columns)</p>
  
  <pre><code>A1 A2 A3 B1 B2 B3 C1 C2 C3 TT YY ZZ
  11 22 33 44 55 66 77 88 99 23 24 25
  11 22 33 44 55 66 77 88 99 23 24 25
  11 22 33 44 55 66 77 88 99 23 24 25
  11 22 33 44 55 66 77 88 99 23 24 25
  11 22 33 44 55 66 77 88 99 23 24 25
  11 22 33 44 55 66 77 88 99 23 24 25
  </code></pre>
  
  <p>TO:</p>
  
  <pre><code>HH JJ KK TT YY ZZ
  11 22 33 23 24 25
  11 22 33 23 24 25
  11 22 33 23 24 25
  11 22 33 23 24 25
  11 22 33 23 24 25
  11 22 33 23 24 25
  44 55 66 23 24 25
  44 55 66 23 24 25
  44 55 66 23 24 25
  44 55 66 23 24 25
  44 55 66 23 24 25
  44 55 66 23 24 25
  77 88 99 23 24 25
  77 88 99 23 24 25
  77 88 99 23 24 25
  77 88 99 23 24 25
  77 88 99 23 24 25
  77 88 99 23 24 25
  </code></pre>
  
  <p>HH, JJ and KK are new columns where I would make a vertical stack of column A, B, C and keeping in horizontal stack TT, YY and ZZ</p>
  
  <pre><code>A1 A2 A3 TT YY ZZ 
  B1 B2 B3 TT YY ZZ
  C1 C2 C3 TT YY ZZ
  </code></pre>
  
  <p>Thanks for your help</p>