title: Custom functions calculated columns mongodb projection
body: <p>I am trying to use projection to get a column calculated using a custom function on columns in collection but I couldn't't figure a way how to do it. What I could do is this:</p>
  
  <pre><code>db.collection.aggregate([$project:{column1:1, calculatedCol: {$literal:[ jaro_Winkler("how to access column name")]}] )
  </code></pre>
  
  <p>The code might have syntax error because I don't have the code with me right now.</p>