mapReduce gives different results in upgraded 2.2.0 - mongodb

Question

I've been using mongodb 2.0.4 in development, and on deploying to production I failed to realize they were running 2.2.0. The mapReduce function that I was using is no longer behaving as it was under 2.0.4, and I can't figure out why.
mongodb 2.0.4 (note: M,F,T,I,C,H,R,D should total 144, and does in this example):
{
"_id" : "",
"value" : {
"tag" : "",
"networth" : 43558505,
"land" : 201837,
"alive" : 144,
"M" : 86,
"F" : 6,
"T" : 5,
"I" : 10,
"C" : 17,
"H" : 4,
"R" : 12,
"D" : 4,
"gdi" : 15
}
}
mongo 2.2.0(m+f+t+i+c+h+r+d totals up to 108, when it should total 144)
{
"_id" : "",
"value" : {
"tag" : "",
"networth" : 43558505,
"land" : 201837,
"alive" : 144,
"M" : 67,
"F" : 5,
"T" : 3,
"I" : 6,
"C" : 13,
"H" : 3,
"R" : 9,
"D" : 2,
"gdi" : 15
}
}
Here is the map/reduce functions I'm using:
// Map function
var map = function() {
var key = this.tag;
var value =
{
tag: this.tag,
networth: this.networth,
land: this.land,
alive: this.alive,
gdi: this.gdi,
gov: this.gov
};
emit(key, value);
};
Reduce function
var reduce = function(k,vals) {
reducedVals = { tag: k, networth: 0, land: 0, alive: 0, M: 0, F: 0, T: 0, I: 0, C: 0, H: 0, R: 0, D: 0, gdi: 0 };
for (var i = 0; i < vals.length; i++){
reducedVals.networth += vals[i].networth;
reducedVals.land += vals[i].land;
reducedVals.alive += vals[i].alive;
reducedVals.gdi += vals[i].gdi;
if (vals[i].gov == "M") reducedVals.M = reducedVals.M + 1;
if (vals[i].gov == "F") reducedVals.F = reducedVals.F + 1;
if (vals[i].gov == "T") reducedVals.T = reducedVals.T + 1;
if (vals[i].gov == "I") reducedVals.I = reducedVals.I + 1;
if (vals[i].gov == "C") reducedVals.C = reducedVals.C + 1;
if (vals[i].gov == "H") reducedVals.H = reducedVals.H + 1;
if (vals[i].gov == "R") reducedVals.R = reducedVals.R + 1;
if (vals[i].gov == "D") reducedVals.D = reducedVals.D + 1;
}
return reducedVals;
};
Perform the map reduce
collection.mapReduce(map, reduce, {out: {replace : 'alliances'}, query: {"alive":1}}, function(err, collection) {
// Mapreduce returns the temporary collection with the results
db.close();
});
So brief rundown.. the collection has a bunch of scores, in this format:
"alive" : 1,
"countryNumber" : 47,
"deleted" : 0,
"gdi" : 0,
"gov" : "C",
"land" : 20111,
"name" : "AtheistCelebratingXmas",
"networth" : 9793082,
"protection" : 0,
"rank" : 1,
"resetid" : 407,
"serverid" : 9,
"tag" : "Evolve",
"vacation" : 0
I'm essentially grouping by tag, summing up the networth, land and alive columns. Then checking the gov column for its value and summing up the totals of D,R,etc. Is there a particular reason I'm missing for why this won't work correctly in 2.2 vs 2.0.4? Either way, will the new aggregate commands do this more easily? I gave it a brief look over, and can get the group by tag, with sums for networth and alive columns to work--but wouldn't know where to begin with the gov column.

Answer 1

The shape of the object you emit from your map function must be the same as the object returned from your reduce function. This is because the results of a reduce call can get fed back into reduce when MongoDB decides to parallelize your map-reduce.
So you need to change your map to assemble the values to emit like this so they have the same structure as what's returned from reduce:
var value = {
"tag" : this.tag,
"networth" : this.networth,
"land" : this.land,
"alive" : this.alive,
"gdi" : this.gdi
};
value[this.gov] = 1;
and then update your reduce function accordingly.
BTW, given enough docs this would have failed in 2.0.4 as well. It's just that 2.2 uses different thresholds for when to parallelize.

Answer 2

I accepted JohnnyHK answer as he answered why my code was not working from one version to another; however, I felt I should post what I modified in the code to resolve the issue.
Map Function:
var map = function() {
var key = this.tag;
var fields = {
tag: this.tag,
networth: this.networth,
land: this.land,
alive: this.alive,
gdi: this.gdi,
M: 0,
F: 0,
T: 0,
I: 0,
C: 0,
H: 0,
R: 0,
D: 0
};
if (this.gov == "M") fields["M"] = 1
else fields["M"] = 0
if (this.gov == "F") fields["F"] = 1
else fields["F"] = 0
if (this.gov == "T") fields["T"] = 1
else fields["T"] = 0
if (this.gov == "I") fields["I"] = 1
else fields["I"] = 0
if (this.gov == "C") fields["C"] = 1
else fields["C"] = 0
if (this.gov == "H") fields["H"] = 1
else fields["H"] = 0
if (this.gov == "R") fields["R"] = 1
else fields["R"] = 0
if (this.gov == "D") fields["D"] = 1
else fields["D"] = 0
emit(key, fields);
};
Reduce Function:
var reduce = function(k,vals) {
reducedVals = { tag: k, networth: 0, land: 0, alive: 0, M: 0, F: 0, T: 0, I: 0, C: 0, H: 0, R: 0, D: 0, gdi: 0};
for (var i = 0; i < vals.length; i++){
reducedVals.networth += vals[i].networth;
reducedVals.land += vals[i].land;
reducedVals.alive += vals[i].alive;
reducedVals.gdi += vals[i].gdi;
reducedVals.M += vals[i].M;
reducedVals.F += vals[i].F;
reducedVals.T += vals[i].T;
reducedVals.I += vals[i].I;
reducedVals.C += vals[i].C;
reducedVals.H += vals[i].H;
reducedVals.R += vals[i].R;
reducedVals.D += vals[i].D;
}
return reducedVals;
};