db.runCommand({ mapreduce: "c",
map : function Map() {
emit(
this.province, // how to group
{country:this.country,province:this.province,city:this.city,temprature:this.temprature,weather:this.weather} // associated data point (document)
);
},
reduce : function Reduce(key, values) {
var reduced={country:{},province:{},city:[],temprature:[],weather:[]};