Database
[{id:1,category:"food",score:20},{id:2,category:"drink",score:19},{id:3,category:"food",score:50},{id:4,category:"food",score:30}]
Query
db.collection.aggregate([{"$match":{"category":"food"}},{"$sort":{"score":-1}},{"$group":{"_id":"null","data":{"$push":"$$ROOT"}}},{"$project":{"id":1,"rank4":{"$indexOfArray":["$data.id",4]},"rank3":{"$indexOfArray":["$data.id",3]}}}])