This question is turned into a Q&A, because I had struggle finding the answer, and think it can be useful for others

我有一个JavaScript数组值,需要在JavaScript中计算它的Q2(第50百分位数,即MEDIAN),Q1(第25百分位数)和第3百分位数(第75百分位数).

解决方法:

在搜索了很长时间后,找到了不同的版本,给出了不同的结果,我在Bastian Pöttner’s web blog上找到了这个不错的代码段,但对于PHP.对于相同的价格,我们得到数据的平均值和标准差(对于正态分布)……

PHP版本

//from https://blog.poettner.de/2011/06/09/simple-statistics-with-php/

function Median($Array) {
  return Quartile_50($Array);
}

function Quartile_25($Array) {
  return Quartile($Array, 0.25);
}

function Quartile_50($Array) {
  return Quartile($Array, 0.5);
}

function Quartile_75($Array) {
  return Quartile($Array, 0.75);
}

function Quartile($Array, $Quartile) {
  sort($Array);
  $pos = (count($Array) - 1) * $Quartile;

  $base = floor($pos);
  $rest = $pos - $base;

  if( isset($Array[$base+1]) ) {
    return $Array[$base] + $rest * ($Array[$base+1] - $Array[$base]);
  } else {
    return $Array[$base];
  }
}

function Average($Array) {
  return array_sum($Array) / count($Array);
}

function StdDev($Array) {
  if( count($Array) < 2 ) {
    return;
  }

  $avg = Average($Array);

  $sum = 0;
  foreach($Array as $value) {
    $sum += pow($value - $avg, 2);
  }

  return sqrt((1 / (count($Array) - 1)) * $sum);
}

基于作者的评论,我只是写了一个肯定会有用的JavaScript翻译,因为令人惊讶的是,几乎不可能在网上找到一个等价的JavaScript,否则需要像Math.js这样的其他库.

JavaScript版本

//adapted from https://blog.poettner.de/2011/06/09/simple-statistics-with-php/
function Median(data) {
  return Quartile_50(data);
}

function Quartile_25(data) {
  return Quartile(data, 0.25);
}

function Quartile_50(data) {
  return Quartile(data, 0.5);
}

function Quartile_75(data) {
  return Quartile(data, 0.75);
}

function Quartile(data, q) {
  data=Array_Sort_Numbers(data);
  var pos = ((data.length) - 1) * q;
  var base = Math.floor(pos);
  var rest = pos - base;
  if( (data[base+1]!==undefined) ) {
    return data[base] + rest * (data[base+1] - data[base]);
  } else {
    return data[base];
  }
}

function Array_Sort_Numbers(inputarray){
  return inputarray.sort(function(a, b) {
    return a - b;
  });
}

function Array_Sum(t){
   return t.reduce(function(a, b) { return a + b; }, 0); 
}

function Array_Average(data) {
  return Array_Sum(data) / data.length;
}

function Array_Stdev(tab){
   var i,j,total = 0, mean = 0, diffSqredArr = [];
   for(i=0;i<tab.length;i+=1){
       total+=tab[i];
   }
   mean = total/tab.length;
   for(j=0;j<tab.length;j+=1){
       diffSqredArr.push(Math.pow((tab[j]-mean),2));
   }
   return (Math.sqrt(diffSqredArr.reduce(function(firstEl, nextEl){
            return firstEl + nextEl;
          })/tab.length));  
}