title: how to accumulate several column and do summation?
body: <p>I want to combine 15 columns which have 3 same columns (so it has 5 same copies of it). My data is looked like this (for the example, it's only 3 copies of it in order to make it simple)</p>
  
  <pre><code>   date     sku1  prod1  tot1  sku2  prod2  tot2  sku3  prod3  tot3
  01/02/2019  100     a    100
  01/02/2019  100     a    200    101    b     50
  02/02/2019  101     b    100
  02/02/2019  101     b     50    102    c    100   100     a     50
  02/02/2019  102     c     50
  </code></pre>
  
  <p>to be like this</p>
  
  <pre><code>   date     sku  all_prod  total
  01/02/2019  100     a       300
  01/02/2019  101     b        50
  02/02/2019  101     b       150
  02/02/2019  102     c       150
  02/02/2019  100     a        50
  </code></pre>
  
  <p>anyone know how to done this? Thanx so much in advance</p>