title: List most prevalent values with their corresponding sum
body: <p>I want to get top N most prevalent values of a field in a CSV file
  with their sum in another field. How may I do that with awk?</p>
  
  <p>Suppose my file is:</p>
  
  <pre><code>v1,45
  v3,20
  v2,500
  v3,100
  v2,200
  v1,55
  v3,50
  v1,10
  </code></pre>
  
  <p>and I need N=2 most occurring field 1 values with their sum of corresponding field2 values
  in this case output would be:</p>
  
  <pre><code>v1,110
  v3,170
  </code></pre>