计算数组中每个值在该数组中出现的次数(javascript) [英] Counting the number of times each value in the array appears in that array (javascript)

问题描述

我有一个问题，我应该如何对数组执行一些数学运算.如果这是一个基本问题，我很抱歉，javascript不是我最强的语言，并且在我最好的日子里，我是一名普通的程序员.

I've got a question as to how I should go about performing some math over an array. My apologies if this is a basic question, javascript is not my strongest language and I'm a mediocre programmer on my best days.

我有一个值数组，作为分析的一部分，我正在执行mann-kendall检验，但是我碰到了要计算方差的墙.( http://vsp.pnnl.gov/help/Vsample/Design_Trend_Mann_Kendall.htm步骤6)

I have an array of values and as part of an analysis, I'm performing a mann-kendall test, but I've hit a wall where I'm calculating the variance. (http://vsp.pnnl.gov/help/Vsample/Design_Trend_Mann_Kendall.htm Step #6)

基本上，我想计算数组中每个值出现在该数组中的次数.因此，例如在世界的特定像素处，数组可能看起来像:

Essentially, I'd like to count the number of times each value in the array appears in that array. So for instance at a particular pixel of the world, the array might look like:

[1, 1, 0.7, 0.3, 1, 0.8, 1, 0.8, 0.7, 1]  

我需要计算一个特定值出现的次数，然后运行表达式
表达式(值*(值-1)*(值* 2 + 5));

I need to count the number of times a particular value appears, then run the expression
Expression(value*(value-1)*(value*2+5));

因此，对于该数组，我想要不同的值计数...

So for that array, I want the distinct value counts...

1: 5  
0.7: 2  
0.8: 2  
0.3: 1  

然后计算这些关系"的值作为表达式的一部分...

And then compute the value of those "ties" as a part of the expression...

5 * (5-1) * (5*2 -5) +   
2 * (2-1) * (2*2 -5) +   
2 * (2-1) * (2*2 -5) +   
1 * (1-1) * (1*2 -5)  

一些注意事项:

• 这是用于地图的Javascript(例如Google Map Engine)，因此某些更标准的Javascript答案可能不起作用(我已经尝试了其他SO线程的一些脚本变体(推荐答案

  var arr = [1, 1, 0.7, 0.3, 1, 0.8, 1, 0.8, 0.7, 1];
  document.write(compute(arr));
   
  function compute(arr){
      freq = {};
      for(var i=0; i<arr.length; i++){
          freq[arr[i]] = (freq[arr[i]] || 0) + 1;
      }
      
      var sum = 0;
      for(var i in freq){
          sum += freq[i]*(freq[i]-1)*(freq[i]*2-5);
      }
      return sum;
  }

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