title: Multiple group in single query of MongoDB
body: <p>I've a set of multiple records with different "label" and "purpose" </p>
  
  <pre><code>{
      billNumber: "",
      _id: "5c94fbc222ac2a0017e70859",
      label: "5c94fb7722ac2a0017e70857",
      purpose: "Purchasing",
      date: "2019-03-27T00:00:00.000Z",
      amount: 200000
  },
  {
      billNumber: "",
      _id: "5c95e300a634360017498c39",
      label: "5c94fba222ac2a0017e70858",
      purpose: "Deposit",
      date: "2018-05-08T00:00:00.000Z",
      amount: 792
  }
  </code></pre>
  
  <p>I want to group my records first with "label" id and then with "purpose" and show the result like:</p>
  
  <pre><code>[
      {
          "label" : "5c94fb7722ac2a0017e70857",
          "balance" : {
              "purchasing" : 240404,
              "deposit" : 4342
          }
      },
      {
          "label" : "5c94fb7722ac2rewt17e7084w58",
          "balance" : {
              "Purchasing" : 455356,
              "Deposit" : 56577
          }
      },
  ]
  </code></pre>