MongoDB Exercise - Find the highest score for each restaurant

Write a MongoDB query to find the highest score for each restaurant.

Structure of 'restaurants' collection :

{
  "address": {
     "building": "1007",
     "coord": [ -73.856077, 40.848447 ],
     "street": "Morris Park Ave",
     "zipcode": "10462"
  },
  "borough": "Bronx",
  "cuisine": "Bakery",
  "grades": [
     { "date": { "$date": 1393804800000 }, "grade": "A", "score": 2 },
     { "date": { "$date": 1378857600000 }, "grade": "A", "score": 6 },
     { "date": { "$date": 1358985600000 }, "grade": "A", "score": 10 },
     { "date": { "$date": 1322006400000 }, "grade": "A", "score": 9 },
     { "date": { "$date": 1299715200000 }, "grade": "B", "score": 14 }
  ],
  "name": "Morris Park Bake Shop",
  "restaurant_id": "30075445"
}

Query:

db.restaurants.aggregate([{
    $unwind: "$grades"
  },
  {
    $group: {
      _id: "$name",
      highest_score: {
        $max: "$grades.score"
      }
    }
  }
])

Output:

{ _id: 'Cucina Gourmet', highest_score: 17 },
{ _id: 'Picanteria El Botecito', highest_score: 13 },
{ _id: 'LefkosPygos Cafe', highest_score: 10 },
{ _id: 'Bull Head Tavern', highest_score: 11 },
{ _id: "Rosa'S Pizza", highest_score: 39 },
{ _id: 'Cafe Loup', highest_score: 19 },
{ _id: 'Cafe Rustico Ii', highest_score: 13 },
{ _id: 'Bliss Street Station Restaurant', highest_score: 12 },
{ _id: 'Hallmark Deli', highest_score: 10 },
{ _id: 'Starbucks Coffee (Store #7555)', highest_score: 13 },

.....

Explanation:

The $unwind operator deconstructs the grades array field of each document in the restaurants collection into multiple documents, one for each element in the array.

The $group operator groups the documents by the name field and calculates the maximum score in the grades array for each group. The result is returned as a new document with two fields: _id, which contains the value of the name field for the group, and highest_score, which contains the maximum score in the grades array for that group.

Note: This output is generated using MongoDB server version 3.6

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