用reddit排序算法对mongodb进行排序 [英] Sorting mongodb by reddit ranking algorithm

问题描述

这是根据Reddit的排名算法对项目进行排名的js代码。

Here is a js code to rank items according to Reddit's ranking algorithm.

我的问题是：如何使用此代码对我的mongodb文档进行排名？

My question is: how do I use this code to rank my mongodb documents ?

（ 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;
}

推荐答案

您可以使用mapReduce：

Well you can use 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 );

};

运行mapReduce（不带减速器）：

And the run the mapReduce (without a reducer):

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

当然假设您的集合包含 ups ，缩减和日期。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分类结果。

And of course presuming that your "collection" has the fields for ups, downs and date. Of course the "rankings" need to be emitted in a way that is "unique" otherwise you need a "reducer" to sort out the results.

但一般来说应该做的。

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