MongoDB Exercise - Find the cuisine type that is most likely to receive a "C" grade

Write a MongoDB query to find the cuisine type that is most likely to receive a 'C' grade.

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"},
  {$match: {"grades.grade": "C"}},
  {$group: {_id: "$cuisine", count: {$sum: 1}}},
  {$sort: {count: -1}}
])

Output:

{ _id: 'American ', count: 172 },
{ _id: 'Italian', count: 59 },
{ _id: 'Pizza', count: 46 },
  {
    _id: 'Latin (Cuban, Dominican, Puerto Rican, South & Central American)',
count: 29
  },
{ _id: 'Chinese', count: 28 },
{ _id: 'Japanese', count: 27 },
{ _id: 'Pizza/Italian', count: 21 },
{ _id: 'Caribbean', count: 19 },
{ _id: 'Jewish/Kosher', count: 17 },
{ _id: 'Mexican', count: 16 },
{ _id: 'Bakery', count: 15 },
{ _id: 'Hamburgers', count: 14 },
{ _id: 'Indian', count: 11 },
{ _id: 'Thai', count: 9 },
{ _id: 'French', count: 8 },
{ _id: 'Delicatessen', count: 7 },
{ _id: 'Korean', count: 7 },
{ _id: 'Café/Coffee/Tea', count: 7 },
{ _id: 'Spanish', count: 6 },
{ _id: 'Irish', count: 6 },
.....

Explanation:

The said query in MongoDB returns the count of "C" grades for each cuisine type in the restaurants collection.

The $unwind stage deconstructs the grades array in each document into separate documents, one for each element of the array.

The $match stage filters the documents to only include those with a "C" grade.

The $group stage groups the resulting documents by cuisine type and counts the number of documents for each cuisine type.

The $sort stage sorts the grouped documents in descending order by the count.

Note: This output is generated using MongoDB server version 3.6

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