m101js.hw5.3.js

gistfile1.js

db.grades.aggregate([
    {$unwind: '$scores'},
    {$match:
        {"scores.type": {$in: ["exam", "homework"]}}},
    {$group:
        {
            _id: {
                'student_id': '$student_id',
                'class_id': '$class_id'
            },
            avg_score: {$avg: '$scores.score'}
        }
    },
    {$group: 
        {
            _id: {
                'class_id': '$_id.class_id'
            },
            avg_score: {$avg: '$avg_score'}
        }
    },
    {$sort:
        {'avg_score': -1}
    }
])