title: Concatenate fields in a csv file
body: <p>I have a csv file with 20 fields: v1:v20. Is there any way to add another field after v5 which would be the concatenation of fields 2 to 5? For example, let's say the file header is:</p>
  
  <pre><code>v1, v2, v3, v4, v5, v5, v7,...
  a,  b,  c,  d,  e,  f,  g,....
  </code></pre>
  
  <p>I want it to look like this:</p>
  
  <pre><code>v1, v2, v3, v4, v5, new.field, v5, v7,...
  a,  b,  c,  d,  e,   bcde,     f,  g,...
  </code></pre>