Javascript ES6 计算对象数组的总和

Question

我有多个对象数组，它们具有字符串属性 "CountType" 和数字属性 "ItemCount"。

必须通过"CountType" 属性将对象相加以计算所有项目的总数。

例如，我需要知道 Volumes、Sheets、Photos 等的总数。

尝试 #1:我尝试的这段代码返回 0。这可能是因为我需要循环遍历外部数组以对嵌套数组进行比较。

function sumByProperty(items, prop) {
  if (items == null) {
      return 0;
  }
  return items.reduce(function (a, b) {
      return b[prop] == null ? a : a + b[prop];
  }, 0);
}

输入

项目数

[
    [
      {"CountType":"Volumes","ItemCount":3},
      {"CountType":"Sheets","ItemCount":6},
      {"CountType":"Photos","ItemCount":3},
      {"CountType":"Boxes","ItemCount":1},
      {"CountType":"Other","ItemCount":2}
    ],
    [
      {"CountType":"Volumes","ItemCount":1},
      {"CountType":"Sheets","ItemCount":1},
      {"CountType":"Photos","ItemCount":3},
      {"CountType":"Boxes","ItemCount":0},
      {"CountType":"Other","ItemCount":1}
    ],
    [
      {"CountType":"Volumes","ItemCount":1},
      {"CountType":"Sheets","ItemCount":0},
      {"CountType":"Photos","ItemCount":3},
      {"CountType":"Boxes","ItemCount":4},
      {"CountType":"Other","ItemCount":5}
    ]
]

DEISRED 输出

总计数

[
  {"CountType":"Volumes","ItemCount":5},
  {"CountType":"Sheets","ItemCount":7},
  {"CountType":"Photos","ItemCount":9},
  {"CountType":"Boxes","ItemCount":5},
  {"CountType":"Other","ItemCount":8}
]

更新:这是我尝试运行函数的方式:

https://jsfiddle.net/yd051o76/2/

Answer 1

Possibly that is because I need to loop through the outer array to do the comparison across the nested arrays.

事实上，您可以展平数组:

 function sumByProperty(items, prop) {
   return items.flat().reduce(function (a, b) {
     return b[prop] == null ? a : a + b[prop];
   }, 0);
 }

 const result = [
   { CountType: "Volumes", ItemCount: sumByProperty(input, "Volumes"), },
   //...
 ];

但我宁愿使用哈希表进行动态分组，这样您只需迭代一次，而无需命名所有属性:

  const hash = new Map();

   for(const { CountType, ItemCount } of input.flat())
      hash.set(CountType, (hash.get(CountType) || 0) + ItemCount);

  const result = [...hash.entries()].map(([CountType, ItemCount]) => ({ CountType, ItemCount }));