如何在MongoDB上做旋转？

{
  "_id": 1,
  "name": "Alice",
  "subject": "Math",
  "score": 90
},
{
  "_id": 2,
  "name": "Bob",
  "subject": "Math",
  "score": 80
},
{
  "_id": 3,
  "name": "Alice",
  "subject": "English",
  "score": 85
},
{
  "_id": 4,
  "name": "Bob",
  "subject": "English",
  "score": 75
}

{
  "_id": 1,
  "name": "Alice",
  "Math": 90,
  "English": 85
},
{
  "_id": 2,
  "name": "Bob",
  "Math": 80,
  "English": 75
}

db.students.aggregate([
  {
    $group: {
      _id: "$name",
      Math: { $max: { $cond: [{ $eq: ["$subject", "Math"] }, "$score", null] } },
      English: { $max: { $cond: [{ $eq: ["$subject", "English"] }, "$score", null] } }
    }
  },
  {
    $project: {
      _id: 1,
      name: "$_id",
      Math: 1,
      English: 1
    }
  },
  {
    $replaceRoot: {
      newRoot: "$$ROOT"
    }
  }
])