function query_month(i, data, callback) {
    query = M_logs.aggregate([
        {
            "$match" : {
                "time" : {
                    "$gt" : new Date(now.getFullYear(), i, 1).getTime() / 1000,
                    "$lt" : new Date(now.getFullYear(), i + 1, 1).getTime() / 1000
                },
                "from" : "mobile"
            }
        },
        {
            "$group" : {
                "_id" : "$is_newuser",
                "count" : { "$sum" : 1 }
            }
        }
    ]);

    query.exec(function (err, result) {
        if(err) {
            console.log('ERR: ' + err);
            result = [];
        }
        if(result.length === 0) {
            result = [{ _id: 'n', count: 0 }, { _id: 'y', count: 0 }];
        }
        data[i] = result;
        if(i < now.getMonth()) {
            query_month(i + 1, data, callback);
        } else {
            callback(data);
        }
    });
}