Cálculo do I3

aggregationI3.js

//Speed up MongoDB Map Reduce, http://edgystuff.tumblr.com/post/54709368492 
//MongoDB as a pure in-memory, http://edgystuff.tumblr.com/post/49304254688 


db.notas.ensureIndex({c:1});
//db.notas.ensureIndex({p:-1}); //6786ms
db.notas.ensureIndex({a:1});

db.alunos.find().forEach(function(a){ db.notas.update({c:a._id,p:{$gte:a.p}},{$set:{v1:1}},{multi:true}) });
db.grade.find().forEach(function(g){ db.notas.update({a:g.ca},{$set:{v2:1}},{multi:true}) });

//db.notas.aggregate( //7.136ms
var res = db.runCommand( //1.203ms
   { aggregate: "notas", pipeline: [
       { $match : { v1 : 1 , v2: 1 } },
       { $sort : { p : -1 } },
       { $group :
            { _id : { c : "$c", a:"$a" } ,
             n : { $first : "$n" } } ,
        },
	{
	 $group :
            { _id : { c : "$_id.c", n:"$n" } ,
             value : { $sum : 1 } },
	},
 	{ $group :
                { _id : "$_id.c",
                ns: { $push: { n : "$_id.n" , v: "$value" } } }
        },
        { $out: "notas_group"}
   ], allowDiskUse: true, }
);

//printjson(res);

var map = function(){
	var nota = { A:0, B:0, C:0, D:0, FF:0, X:0 };
	this.ns.forEach(function(n){
		nota[n.n] = n.v;
	});
	emit(this._id,nota);
};

var reduce = function(key, notas) { return notas; }

var finalize = function(key, notas){
    var sum = notas.FF + notas.X + notas.D + notas.C + notas.B + notas.A;
    var div = notas.FF + (notas.X/2) + (notas.D/3) + (notas.C/6) + (notas.B/8) + (notas.A/10);
    notas.I3 = sum / div;
    return notas;
}

db.notas_group.mapReduce( map, reduce, //2.022ms
                        { finalize: finalize,
                          out: { replace : "alunoI3" },
                          //sort: { "_id.c":1 },
                          jsMode: true,
                        });