title: Mongo $group with $project
body: <p>I am trying to get keyword count along with <code>parentId</code>, <code>categioryId</code> and <code>llcId</code>.
  My db is </p>
  
  <pre><code>{
      "_id" : ObjectId("5673f5b1e4b0822f6f0a5b89"),
      "keyword" : "electronic content management system",
      "llcId" : "CL1K9B",
      "categoryId" : "CL1K8V",
      "parentId" : "CL1K8V",
  
  }
  </code></pre>
  
  <p>I tried <code>$project</code> with <code>$group</code></p>
  
  <pre><code>db.keyword.aggregate([
      {
          $group: {
              _id: "$llcId",
              total: {$sum: 1},
          }
      },
      {
          $project: {
              categoryId: 1, total: 1
          }
      }
  ])
  </code></pre>
  
  <p>And it gives me a result like </p>
  
  <pre><code>{ "_id" : "CL1KJQ", "total" : 17 }
  { "_id" : "CL1KKW", "total" : 30 }
  </code></pre>
  
  <p>But I need actual data in result also e.g. <code>llcId</code>, <code>categoryId</code>, <code>keyword</code>, <code>total</code>. I tried to display <code>cetgoryId</code> and keyword by using <code>$project</code> but it displays only <code>_id</code> and total. What I am missing?</p>