title: mongodb aggregation query, using projection, $size,$split
body: <p>i have to make a query, so in my query i must to show only  when the size is one; and in my projection i show the results , and i have the query but only show all the sizes, but i only need to show when the size is one, i ve no idea how to make it. and i used a projection.
  this is a single doc:
  <a href="https://i.stack.imgur.com/TBzST.png" rel="nofollow noreferrer">document</a></p>
  
  <p>and my query is this:</p>
  
  <pre><code>db.movies.aggregate([
  {"$project":
    {
      "_id": 0,
      "longi":{$size:{ $split: [ "$title", " " ]}}
    }
      }]);
  </code></pre>
  
  <p>and the result is this:</p>
  
  <pre><code>{ "longi" : 2 }
  
  { "longi" : 2 }
  
  { "longi" : 6 }
  
  { "longi" : 11 }
  
  { "longi" : 2 }
  
  { "longi" : 2 }
  
  { "longi" : 6 }
  
  { "longi" : 2 }
  
  { "longi" : 1 }
  
  { "longi" : 4 }
  
  { "longi" : 5 }
  
  { "longi" : 3 }
  
  { "longi" : 5 }
  
  { "longi" : 3 }
  
  { "longi" : 3 }
  
  { "longi" : 5 }
  
  { "longi" : 4 }
  
  { "longi" : 5 }
  
  { "longi" : 1 }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/fLZ0D.png" rel="nofollow noreferrer">res</a>
  but i just want to show  when the size is one</p>