borrar el registro de la tarea con la nota mas baja de cada estudiante en la BD MongoDB

prueba.rb

require "mongo"

connection = Mongo::Connection.new("localhost", 27017)

db = connection.db("students")

coll = db.collection("grades")

199.times do |n|
  doc = coll.find("student_id" => n, "type" => "homework").sort(:score => :asc).limit(1)

  doc.each { |i| coll.remove(i) }
end