使用JS在Json数组中的相同ID的总和 [英] Sum values of same Id in a Json Array using JS

问题描述

我有一个ID和年龄如下的json数组

I have a json array with Id and age as follows

var arrayVal = [{id:"1", age: 20},{id:"2", age: 30},{id:"2", age: "20"},{id:"3", age: 20},{id:"5", age: 10}];

我想获取属于相同ID的年龄总和，如下所示：

I want to get sum of age which belong to same id which will be as follows

1 = 20
2 = 50
3 = 20
5 = 10

请找到以下代码

$scope.TestFunc = function()
{
var tot = 0;
var arrayVal = [{id:"1", age: 20},{id:"2", age: 30},{id:"2", age: "20"},{id:"3", age: 20},{id:"5", age: 10}];
for(var i=0; i <arrayVal.length; i++ )
{
  for(var j=1; j<arrayVal.length - i; j++ )
  {
    if(arrayVal[i].id == arrayVal[j].id)
    {
      tot = arrayVal[i].age.valueOf() + arrayVal[j].age.valueOf();
    }
    else{
      tot = tot + arrayVal[i].age;
    }
  }
}
console.log("-----total----"+tot);
}

我没有收到预期的输出。控制台将输出显示为202020。上面的代码出了什么问题？

I don't receive the expected output. the console shows the output as 202020. What has gone wrong in the above code?

推荐答案

使用简单的 reduce（） 操作：

With a simple reduce() operation:

const array = [{id:"1", age: 20},{id:"2", age: 30},{id:"2", age: "20"},{id:"3", age: 20},{id:"5", age: 10}];

const ages = array.reduce((a, {id, age}) => (a[id] = (a[id] || 0) + +age, a), {});

console.log(ages);

除了 reduce 解决方案更加紧凑和声明性外，所提供代码的主要问题还在于 coercion 。 age 值之一具有字符串 20 ，强制随后的 + 操作应解释为字符串连接。

Besides the reduce solution being more compact and declarative, the main problem with the code provided is due to coercion. One of the age values has the string "20", forcing the subsequent + operations to be interpreted as string concatenation.

此答案可避免使用 + age ，将 age 强制为 Number （可以通过执行明确显示数字（年龄））。

This answer avoids this unexpected side-effect using the +age, forcing age to be a Number (this could be made explicit by doing Number(age) instead).

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