mongodb - How to convert this map reduce in aggregate framework? -

i've still done map/reduce/finalize function using mongodb.

this how need mongodb executes aggregation:

db.house_results.mapreduce(function(){     emit(this.house_name.tolowercase(),this);     },function(key,values){         var house = {name:key,address:"",description:"",photo:[],lat:0,lng:0,rooms:[]};         values.foreach(function(house_val) {            /*address*/             if(house.address=="")               house.address = house_val.house_address;             /*photo*/            if(!house_val.photo in house.photo)               house.photo.push(house_val.house_photo);                    /*description*/            if(house.description=="")               house.description = house_val.house_description;              /*lat - lng*/            if(house.lat==0 || house.lng==0){               var house_position = house_val.house_position;               if(house_position && house_position.lat && house_position.lng){                  house.lat = house_position.lat;                   house.lng = house_position.lng;               }            }            if(house.lat==0 || house.lng==0){               if(house_val.house_lat && house_val.house_lng){                  house.lat = house_val.house_lat;                   house.lng = house_val.house_lng;               }            }             if(house_val.rooms)                 house.rooms.push(house_val.rooms);           });          return house;     },     {          out   : "map_reduce_house_test",         finalize:function(key,house_val){             if(house_val.address==undefined){ // 1 result in map function -> reduce function ignored -> finalize solution                var house = {name:key,address:"",description:"",photo:[],lat:0,lng:0,rooms:[]};                /*address*/                if(house.address=="")                  house.address = house_val.house_address;                 /*photo*/                if(!house_val.photo in house.photo)                   house.photo.push(house_val.house_photo);                        /*description*/                if(house.description=="")                   house.description = house_val.house_description;                  /*lat - lng*/                if(house.lat==0 || house.lng==0){                   var house_position = house_val.house_position;                   if(house_position && house_position.lat && house_position.lng){                      house.lat = house_position.lat;                       house.lng = house_position.lng;                   }                }                if(house.lat==0 || house.lng==0){                   if(house_val.house_lat && house_val.house_lng){                      house.lat = house_val.house_lat;                       house.lng = house_val.house_lng;                   }                }                 if(house_val.rooms)                   house.rooms.push(house_val.rooms);                 return house;              }else                return house_val;          }     } ); 

is there way simplify functions and/or better same aggregation mongodb's function?

which fastest , simplier method?

thanks!

there isn't going on in mapreduce other taking first values various fields common grouping key , otherwise pushing other values onto arrays.

therefore same aggregation:

db.house_results.aggregate([     { "$group": {         "_id": { "$tolower": "$house_name" },         "name": { "$first": { "$tolower": "$house_name" } },         "photo": { "$push": "$house_photo" },         "address": { "$first": "$house_address" },         "description": { "$first": "$house_description" },         "lat": {             "$max": {                 "$cond": [                    { "$gt": [ "$house_lat", "$house_position.lat" } },                    "$house_lat",                    "$house_position.lat"             }         },         "lng": {             "$max": {                 "$cond": [                    { "$gt": [ "$house_lng", "$house_position.lng" } },                    "$house_lng",                    "$house_position.lng"             }         },         "rooms": { "$push": "$house_rooms" }     }} ]) 

the real difference there conditional handling of "lat" , "lng" output using $cond operator.

noting "_id" , "name" have same thing in them, map reduce doing.

take @ aggregation operators reference, data should rather it's present form, appears de-normalized dump somewhere.

also reference, isn't affecting in case, wrong way write mapreduce. output "map" function different "reduce" function, notably arrays.

even though these have 1 element in them "should" emitted array element "map" function , treated if array element "reduce" function.

this because larger "grouping", not matching key values sent reduce function @ once, , reducer can called combine other values emitted "map" "reduce" function reduced output. how large data handling, , arrays run risk of output this, un-expected embedding of array within array:

[ [4,5,6], 7, 8, 9 ] 

but covered in the documentation read carefully.

at rate, aggregation pipeline ( 1 stage) perform faster present operation. change data possible.