//在Mongodb的MapReduce中可以使用JS的Math函数嘛，可以使用new Date()嘛，回答是肯定的！

$map = 'function(){

            var key = {
                advert_id     : this.advert_id,
                district_code : this.district_code,
                lng           : (Math.ceil( (this.lng - 73.40) /0.02 ) * 0.02 + 73.38).toFixed(2),
                lat           : (Math.ceil( (this.lat -  3.52) /0.02 ) * 0.02 + 3.50).toFixed(2),
                hours         : (new Date(this.datetime * 1000)).getHours()
            };

            var values = {
                amount:        this.amount,
                number:        1,
                advertiser_id: this.advertiser_id
            };

            emit(key, values);
        }';

$reduce = 'function(key, values){
            var result = {amount:0, number:0, advertiser_id:0};

            for(var i in values) {
                result.advertiser_id  = values[i].advertiser_id;
                result.amount        += values[i].amount;
                result.number        += values[i].number;
            }
            return result;
        }';

$query    = null;