用reddit排序算法对mongodb进行排序

Question

这是一个根据Reddit的排名算法对项目进行排名的js代码.

我的问题是:如何使用此代码对我的mongodb文档进行排名？

(Reddit的排名算法)

function hot(ups,downs,date){
    var score = ups - downs;
    var order = log10(Math.max(Math.abs(score), 1));
    var sign = score>0 ? 1 : score<0 ? -1 : 0;
    var seconds = epochSeconds(date) - 1134028003;
    var product = order + sign * seconds / 45000;
    return Math.round(product*10000000)/10000000;
}
function log10(val){
  return Math.log(val) / Math.LN10;
}
function epochSeconds(d){
    return (d.getTime() - new Date(1970,1,1).getTime())/1000;
}

Answer 1

那么你可以使用mapReduce:

var mapper = function() {

    function hot(ups,downs,date){
        var score = ups - downs;
        var order = log10(Math.max(Math.abs(score), 1));
        var sign = score>0 ? 1 : score<0 ? -1 : 0;
        var seconds = epochSeconds(date) - 1134028003;
        var product = order + sign * seconds / 45000;
        return Math.round(product*10000000)/10000000;
    }

   function log10(val){
      return Math.log(val) / Math.LN10;
   }

   function epochSeconds(d){
       return (d.getTime() - new Date(1970,1,1).getTime())/1000;
   }

   emit( hot(this.ups, this.downs, this.date), this );

};

并运行mapReduce(没有reducer):

db.collection.mapReduce(
    mapper,
    function(){},
    {
        "out": { "inline": 1 }
    }
)

当然假设你的"集合"有字段ups,downs和date.当然,"排名"需要以"独特"的方式发出,否则你需要一个"减速器"来整理结果.

但总的来说,应该做的工作.