M101J-HW2.2 - using yet-to-be-taught aggregation framework

mongoshell.js

var cursor = db.grades.aggregate([{$group: {_id: "$student_id", minScore: {$min:"$score"}}}]);
while (cursor.hasNext()) { 
  var doc = cursor.next(); 
  db.grades.remove({student_id: doc["_id"], score: doc["minScore"]}); 
}