Pecha Kucha slides about MongoDB

10. var scores=db.grades.find({"type":"homework"}).sort({"student_id":1,"score":1})
var previous_id
var i=0
while(scores.hasNext()) {
var score=scores.next()
var student_id=score.student_id
if (student_id !== previous_id) {
i++
previous_id = student_id
db.grades.remove({"_id":score._id},1)
}
}

11. explain()