Map Reduce

mr1

coll.mapReduce(
	//map
	function(){
		emit(this.tag, {tag_date: this.tag_date, count:this.count});
	},
	// reduce
	function(key, values){
		var obj = {value: []};
		for(var i in values){
			obj.value.push({tag_date:values[i].tag_date, count:values[i].count});
		}
		return obj;
	},
	{out:{inline:1}},
	function(error, results, stats)
	{
		if(error) callback(error);
		else{
			//print(results);
			callback(null,results);
		}
	});