homework_2_2.py

# 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.
import pymongo
import sys

# establish a connection to the database
connection = pymongo.Connection("mongodb://localhost", safe=True)

# get a handle to the school databse
db=connection.students
grades = db.grades

def find_and_remove():

	query = {'type':'homework'}

	try:
		all_homework = grades.find(query)
		sorted_homework = all_homework.sort([('student_id', pymongo.ASCENDING),('score',pymongo.ASCENDING)])

	except:
		print "Unexpected error:", sys.exc_info()[0]

	sanity = 0
	current_student = 0

	for doc in sorted_homework:
		if doc['student_id'] == current_student:
			# print doc
			grades.remove(doc)
			current_student += 1

find_and_remove()