[mongodb mapreduce] add integer value

adding integer value.

input data

db.test2.save({"keyword":"다음",   "freq":10000})

db.test2.save({"keyword":"네이버", "freq":20000})

db.test2.save({"keyword":"다음",   "freq":55555})

map function

m = function(){ emit(this.keyword, { freq_sum:this.freq}); }

reduce function

r = function(key, values){

   var total=0

   values.forEach(function(x){

     total += x.freq_sum

   })

   return {"freq_sum": total };

}

call map/reduce

db.test2.mapReduce(m,r, {out:"mr_result"}) 

out data

db.mr_result.find()

{ "_id" : "네이버", "value" : { "freq_sum" : 20000 } }

{ "_id" : "다음", "value" : { "freq_sum" : 65555 } }