M101P - Homework 2.2

m101p-hw2.2.js

db.grades.distinct('student_id').forEach(function(id) {
  db.grades.findAndModify({
    query: { student_id: id, type: 'homework' },
    sort: { score: 1 },
    remove: true
  });
})

// 600
db.grades.count()

// { "_id" : ObjectId("50906d7fa3c412bb040eb709"), "student_id" : 100, "type" : "homework", "score" : 88.50425479139126 }
db.grades.find().sort({'score':-1}).skip(100).limit(1)

db.grades.find({},{'student_id':1, 'type':1, 'score':1, '_id':0}).sort({'student_id':1, 'score':1, }).limit(5)

// query:
db.grades.aggregate({'$group':{'_id':'$student_id', 'average':{$avg:'$score'}}}, {'$sort':{'average':-1}}, {'$limit':1})