It looks like there's an optimization for map reduce jobs that can result in the wrong key name being returned if there is only a single tuple to process. Notice how the keys for groups 1 and 5 are returned as "thetot" instead of "tot" in the job below.

I believe this is caused by line 103/124 of db/commands/mr.cpp. The workaround appears easy enough but I thought I'd report it.

Thanks

> db.goo.save(

{group:1, amt:5}

);
> db.goo.save(

{group:2, amt:3}

);
> db.goo.save(

{group:2, amt:15}

);
> db.goo.save(

{group:3, amt:1}

);
> db.goo.save(

{group:3, amt:2}

);
> db.goo.save(

{group:3, amt:9}

);
> db.goo.save(

{group:4, amt:1}

);
> db.goo.save(

{group:4, amt:3}

);
> db.goo.save(

{group:4, amt:10}

);
> db.goo.save(

{group:4, amt:12}

);
> db.goo.save(

{group:5, amt:2}

);
>
> map = function(){ emit( this.group,

{ cnt:1, thetot:this.amt }

); }
function () {
emit(this.group,

{cnt:1, thetot:this.amt}

);
}
>
> reduce = function(k, v){
... var r =

{ cnt:0, tot:0 }

;
... v.forEach(function(v)

{ ... r.cnt += v.cnt; ... r.tot += v.thetot ; ... }

)
... return r;
... }
function (k, v) {
var r =

{cnt:0, tot:0}

;
v.forEach(function (v)

{r.cnt += v.cnt;r.tot += v.thetot;}

);
return r;
}
>
> db.goo.mapReduce( map, reduce, { out:

{inline:1}

});
{
"results" : [
{
"_id" : 1,
"value" :

{ "cnt" : 1, "thetot" : 5 }

},
{
"_id" : 2,
"value" :

{ "cnt" : 2, "tot" : 18 }

},
{
"_id" : 3,
"value" :

{ "cnt" : 3, "tot" : 12 }

},
{
"_id" : 4,
"value" :

{ "cnt" : 4, "tot" : 26 }

},
{
"_id" : 5,
"value" :

{ "cnt" : 1, "thetot" : 2 }

}
],
"timeMillis" : 1,
"counts" :

{ "input" : 11, "emit" : 11, "output" : 5 }

,
"ok" : 1,
}