MongoDB Exercise - Find the number of 'A'-rated restaurants by cuisine and borough

Write a MongoDB query to find the count of restaurants that received a grade of 'A' for each cuisine and borough.

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([
  {
    $match: { "grades.grade": "A" }
  },
  {
    $group: {
      _id: { cuisine: "$cuisine", borough: "$borough" },
count: { $sum: 1 }
    }
  },
  {
    $sort: { count: -1 }
  }
]);

Output:

{ _id: { cuisine: 'American ', borough: 'Manhattan' }, count: 731 },
{ _id: { cuisine: 'Italian', borough: 'Manhattan' }, count: 204 },
{ _id: { cuisine: 'American ', borough: 'Queens' }, count: 192 },
{ _id: { cuisine: 'American ', borough: 'Brooklyn' }, count: 190 },
  {
    _id: { cuisine: 'Café/Coffee/Tea', borough: 'Manhattan' },
count: 133
  },
{ _id: { cuisine: 'Pizza', borough: 'Queens' }, count: 80 },
{ _id: { cuisine: 'American ', borough: 'Bronx' }, count: 74 },
{ _id: { cuisine: 'Pizza', borough: 'Manhattan' }, count: 73 },
{ _id: { cuisine: 'Pizza', borough: 'Brooklyn' }, count: 72 },
{ _id: { cuisine: 'French', borough: 'Manhattan' }, count: 68 },
{ _id: { cuisine: 'Japanese', borough: 'Manhattan' }, count: 68 },
.....

Explanation:

The said query in MongoDB that returns a result set that includes each cuisine-borough pair and the count of restaurants that received a grade of 'A' for that pair.

The $match stage filters the restaurants that received a grade of 'A'. The dot notation have used to access the nested grades array.

The $group stage groups the restaurants by cuisine and borough, and calculates the count of restaurants using the $sum operator.

$sort stage sorts the result by the count in descending order, so that the cuisine-borough pairs with the highest counts appear first.

Note: This output is generated using MongoDB server version 3.6

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