title: React/ES6 reduce object
body: <p>I have the following object that holds workouts for specific days:</p>
  
  <pre><code>{
    "2019-03-02": [
      {
          "id": 1,
          "workout_day": "2019-03-02",
          "title": "Swimming",
          "description": "",
          "completed": true,
          "points": 5
      },
      {
          "id": 2,
          "workout_day": "2019-03-02",
          "title": "Running",
          "description": "",
          "completed": false,
          "points": 0
      },
      {
          "id": 3,
          "workout_day": "2019-03-02",
          "title": "Rowing",
          "description": "",
          "completed": true,
          "points": 3
      },
    ],
   "2019-03-05": [...]
  }
  </code></pre>
  
  <p>I want to get a new object that shows for each day how many workouts exist, how much of them have been completed and a sum for the points, like so:</p>
  
  <pre><code>{
    "2019-03-02": {
      "workouts": 3,
      "workouts_completed": 2,
      "total_points": 8
    },
    "2019-03-05: {...}
  }
  </code></pre>
  
  <p>However, I'm totally stuck at the moment. Thanks for help!</p>