title: How to group array of objects by date in swift?
body: <p>Need to group according to date. Response coming is in sorted format. Need to apply a filter on date to group. 
  Response coming from backend: </p>
  
  <pre><code>[
      {
      "date": "date1"
      }, 
      {
      "date": "date1"
      },
      {
      "date": "date1"
      },
      {
      "date": "date2"
      },
      {
      "date": "date2"
      },
      {
      "date": "date3"
      }
  ]
  </code></pre>
  
  <p>Required: </p>
  
  <pre><code>[
      [
          "date": "2017-05-30T12:40:39.000Z",
          "message": [
              {
                  "date_time": 2017-05-30T12: 40: 39.000Z
              }
          ]
      ],
      [
          "date": "2017-05-31T05:43:17.000Z",
          "message": [
              {
                  "date_time": 2017-05-31T05: 43: 17.000Z
              },
              {
                  "date_time": 2017-05-31T05: 44: 15.000Z
              },
              {
                  "date_time": 2017-05-31T05: 44: 38.000Z
              }
          ]
      ]
  ]
  </code></pre>
  
  <p>I have checked multiple answers but wasn't able to find a good solution.</p>