Write a program in the language of your choice that will remove the grade of type "homework" with the lowest score for each student from the dataset that you imported in HW 2.1. Since each document is one grade, it should remove one document per student.

package com.tengen;

import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import com.mongodb.AggregationOutput;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;
import com.mongodb.ServerAddress;

public class Homework23 {

public static void main(String[] args) throws UnknownHostException {
MongoClient client = new MongoClient(new ServerAddress("localhost",
27017));

DB db = client.getDB("students");
DBCollection collection = db.getCollection("grades");

BasicDBObject bdb = new BasicDBObject("type", "homework");

BasicDBObject sort = new BasicDBObject("student_id", 1).append("score",
1);

// DBCursor cur = collection.find(bdb).sort(sort);

List<DBObject> pipeline = new ArrayList<DBObject>();

pipeline.add(new BasicDBObject("$group", new BasicDBObject("_id",
"$student_id")));

AggregationOutput aoup = collection.aggregate(pipeline);

Iterable<DBObject> results = aoup.results();

Iterator<DBObject> itr = results.iterator();
DBCursor cur = null;
try {

while (itr.hasNext()) {
DBObject agdb = itr.next();

bdb.append("student_id", agdb.get("_id"));

cur = collection.find(bdb).sort(sort);

cur.hasNext();

DBObject docToRemove = cur.next();

Double minScore = (Double) docToRemove.get("score");

while (cur.hasNext()) {

DBObject doc1 = cur.next();

if (minScore > (Double) doc1.get("score")) {
minScore = (Double) doc1.get("score");
docToRemove = doc1;
}

}

System.out.println("*********************");
System.out.println(docToRemove);
System.out.println("*********************");

collection.remove(docToRemove);

}

}

finally {
if (cur != null)
cur.close();
}

}

}