title: Consolidate data for weeks to months and quarters, weeks are like W1, W2 and not in date format
body: <p>I've data like this below and want to consolidate data for months and then quarters. Problem is in one month there are 4 weeks and in another month I've 5 weeks, so I can't just apply formula and drag it especially if I've thousands of rows... Any hint would be appreciated.</p>
  
  <p>Data is like this:</p>
  
  <pre><code>Month| Weeks| Sales    
  M1| W1|50    
  M1|W1|30    
  M1| W1|40    
  M1|W1|20    
  M2| W1|50    
  M2|W2|30    
  M2| W3|40    
  M2|W4|20    
  M2|W5|20
  </code></pre>