title: datatables order by number doc and year of doc
body: <p>I don't know how to implement a simple way to sort a column that show me number of doc with trailing year like:</p>
  
  <pre><code>COL 1    COL 2     COL 3    DOC. NR
  ------------------------------------
    x        x          x       2/2020
  ------------------------------------
    x        x          x       3/2020
  ------------------------------------
    x        x          x       4/2021
  ------------------------------------
    x        x          x       1/2022
  ------------------------------------
  </code></pre>
  
  <p>In my example i'd like to sort <code>doc. nr</code> col by asc or desc, based on number of doc (grouped by year).</p>
  
  <p>I tried to set data-order with formula: <code>numberdoc + year</code> but it doesn't work cause, for example, 3 + 2020 is equal to 1 + 2022.... so this way is not correct. Any idea?</p>
  
  <pre><code>&lt;td data-order="2020"&gt;1/2019&lt;/td&gt;
  </code></pre>
  
  <p>Script:</p>
  
  <pre><code>$(document).ready( function () {
    var table = $('#example').DataTable({
       "aaSorting": [[ 1, "desc" ]],
      "columnDefs": [
              {
                  targets: [1],
                  data: {
                      _: "1.display",
                      sort: "1.@data-order",
                      type: "1.@data-order"
                  }
              }
          ]
    });
  } );
  </code></pre>
  
  <p>My fiddle: <a href="http://live.datatables.net/jivekefo/1/edit" rel="nofollow noreferrer">http://live.datatables.net/jivekefo/1/edit</a></p>
  
  <p>Expected (ASC) result:</p>
  
  <pre><code>1/2018
  2/2018
  3/2018
  1/2019
  2/2019
  3/2019
  4/2019
  1/2020
  ...
  </code></pre>