Image Credit SteemWhales.com

Abstract: I have improved this NodeJs script to compute the Median and STD for the members in the Steemit-Wechat Group. It reflects the fact that: the most wealth is posseseed by a few huge whales.

I am planning to put these statistists on the Daily SteemIt Wechat Group Ranking table. The median values help better understand where you are in the big pond (are you really a minnow?)

昨天半夜写的帖子目的是小试 NodeJs 牛刀， @rivalhw 和 @dapeng 给了非常好的建议：平均值不太适合看大众水平，因为：贫富差距在 STEEM的世界里也是非常的明显，目测10%大鱼们掌握了90%的财富，所以如果取平均的话，指标都会偏高，不能反映实际情况。

是不是有很多歌唱比赛评委给分之后，选手的最终得分都得先“去掉一个最高分，去掉一个最低分”？不过在这里，你去掉一个最高最低也没有啥卵用，因为富得流油的远不止一个，穷得只剩下小裤衩的也有很多。

中位数

数学中的中位数（Median）指的是把所有需要统计的数值排序，然后取最中间那个（如果有奇数个数值），如果有偶数个，则取中间两个数来取平均。这个相对能反映出大众水平。

标准方差

标准方差 STD 反映了数据波动的情况，比如如果财富值的标准方差越大，则表示贫富差距大（离平均水平的波动区别）

NodeJs 程序 + SteemIt Wechat API

有了API，我们用 Node.Js 来跑跑，看看什么结果。首先我们通过 prototype 的方式给 Javascript 中的数组来定义以上几个指标：
Let's define these measured by extending Array's prototype in Javascript:

Array.prototype.median = function() {
    var arr = [...this];
    var len = arr.length;
    if (0 == len) {
        return NaN;
    }
    arr.sort(); 
    var mid = Math.floor(len / 2);
    if ((len % 2) == 0) {
        return (arr[mid] + arr[mid - 1]) * 0.5;
    }
    return arr[mid];
}

Array.prototype.mean = function() {
    var total = 0;
    for (var i = this.length - 1; i >= 0; -- i){
        total += this[i];
    }
    return total / this.length;
}

Array.prototype.STD = function() {
   var mean = this.mean();
   var diff = [];
   for (var j = this.length - 1; j >= 0; -- j){
       diff.push(Math.pow((this[j] - mean), 2));
   }
   return (Math.sqrt(diff.reduce((a, b) => a + b) / this.length));
}

然后一样的套路：Then we just need to fetch the ranking table via the handy API.

// @justyy
var request = require("request")
var url = "https://uploadbeta.com/api/steemit/wechat/?cached";
request({
    url: url,
    json: true
}, function (error, response, body) {
    if (!error && response.statusCode === 200) {
        var total_rep = [];
        var total_sbd = [];
        var total_steem = [];
        var total_value = [];
        var total_esp = [];
        var total_vp = [];
        var total_sp = [];
        body.forEach(function(member) {
            total_rep.push(member['rep']);
            total_sbd.push(member['sbd']);
            total_steem.push(member['steem']);
            total_value.push(member['value']);
            total_esp.push(member['esp']);
            total_vp.push(member['vp']);
            total_sp.push(member['sp']);
        });

        console.log("----Median----");
        console.log("Total Members = " + total_rep.length);
        console.log("Median Reputation = " + Math.round(total_rep.median() * 100) / 100);
        console.log("Median SBD = " + Math.round(total_sbd.median() * 100) / 100);
        console.log("Median Steem = " + Math.round(total_steem.median() * 100) / 100);
        console.log("Median Effective SP = " + Math.round(total_esp.median() * 100) / 100);
        console.log("Median SP = " + Math.round(total_sp.median() * 100) / 100);
        console.log("Median Voting Power = " + Math.round(total_vp.median() * 100) / 100);
        console.log("Median Account Value = " + Math.round(total_value.median() * 100) / 100);

        console.log("----Mean----");
        console.log("Mean Reputation = " + Math.round(total_rep.mean() * 100) / 100);
        console.log("Mean SBD = " + Math.round(total_sbd.mean() * 100) / 100);
        console.log("Mean Steem = " + Math.round(total_steem.mean() * 100) / 100);
        console.log("Mean Effective SP = " + Math.round(total_esp.mean() * 100) / 100);
        console.log("Mean SP = " + Math.round(total_sp.mean() * 100) / 100);
        console.log("Mean Voting Power = " + Math.round(total_vp.mean() * 100) / 100);
        console.log("Mean Account Value = " + Math.round(total_value.mean() * 100) / 100);      

        console.log("----STD----");
        console.log("STD Reputation = " + Math.round(total_rep.STD() * 100) / 100);
        console.log("STD SBD = " + Math.round(total_sbd.STD() * 100) / 100);
        console.log("STD Steem = " + Math.round(total_steem.STD() * 100) / 100);
        console.log("STD Effective SP = " + Math.round(total_esp.STD() * 100) / 100);
        console.log("STD SP = " + Math.round(total_sp.STD() * 100) / 100);
        console.log("STD Voting Power = " + Math.round(total_vp.STD() * 100) / 100);
        console.log("STD Account Value = " + Math.round(total_value.STD() * 100) / 100);        
    }
})

然后这是结果：And the results come out pretty quickly using NodeJs

----Median----
Total Members = 173
Median Reputation = 50.83
Median SBD = 154.62
Median Steem = 0
Median Effective SP = 28.15
Median SP = 201.16
Median Voting Power = 93.72
Median Account Value = 2040.61
----Mean----
Mean Reputation = 48.56
Mean SBD = 224.75
Mean Steem = 18.99
Mean Effective SP = 18503.56
Mean SP = 1561.65
Mean Voting Power = 83.07
Mean Account Value = 2436.73
----STD----
STD Reputation = 13.5
STD SBD = 1093.16
STD Steem = 118.9
STD Effective SP = 99019.55
STD SP = 5977.72
STD Voting Power = 21.61
STD Account Value = 9344.65

简单来说：“大众”等级是 50.83，“大众” SP 是201.16，“大众”帐号估值是 2040.61
通过STD我们可以看到，SP，ESP，还有帐号估值的贫富差距还是挺大的。

最后，再广告一下：

SteemIt 好友微信群排行榜
SteemIt 好友微信群文章列表 RSS Feed
SteemIt 编程 Geek 微信群，请联系 @justyy 让我拉你入群。

需要入群者请联系 @tumutanzi 或者 @rivalhw 谢谢。

Originally published at https://steemit.com Thank you for reading my post, feel free to Follow, Upvote, Reply, ReSteem (repost) @justyy which motivates me to create more quality posts.

原文首发于 https://Steemit.com 首发。感谢阅读，如有可能，欢迎Follow, Upvote, Reply, ReSteem (repost) @justyy 激励我创作更多更好的内容。

// Later, it will be reposted to my blogs: justyy.com, helloacm.com and codingforspeed.com 稍后同步到我的中文博客和英文计算机博客。

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The Average, Median, STD of SteemIt Wechat Group 数据初步分析系列 STEEM中文微信群排行榜单 - 中位数，平均，和标准方差

中位数

标准方差

NodeJs 程序 + SteemIt Wechat API

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