The Average, Median, STD of SteemIt Wechat Group

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;
}
 
<h3>How to Compute STD (Standard Deviation) in Javascript?</h3>
STD reflects how big difference the values are from the mean/average.

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));
}

// @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);        
    }
})