title: Count how many times is the same value present in array
body: <p>After grouping in aggregation I have elements that look the following way:</p>
  
  <pre><code>{_id: ID, items: ["yes", "no", "yes", "no", "no", "yes", "no", "no", "no"]}
  </code></pre>
  
  <p>I'd like to project how many times is certain value present in items array</p>
  
  <p>To end up with a document in the format of:</p>
  
  <pre><code>{_id: ID, yes: 3, no: 6}
  </code></pre>