title: How do I display custom formatted nested keys in swimlane ngx-datatable
body: <pre><code>&lt;ngx-datatable
     [rows]="services"
     [columns]="columns"&gt;
  &lt;/ngx-datatable&gt;
  </code></pre>
  
  <p>I can get this to display nested data with:</p>
  
  <pre><code>{ prop: order.product.price }
  </code></pre>
  
  <p>How do you do you display a custom calculation in a row?
  What if I want to apply a fee to the price</p>
  
  <pre><code>{ prop: 'order.product.price + order.fee' }
  </code></pre>
  
  <p>I guess I would need access to the other values in the row.</p>