javascript - 如何从两个对象数组中减去或减去特定值？

Question

说实话，我来这里是为了问一个简单的问题，这让我浪费了太多时间这是示例数据

    const demo1 = [
       { count: 156, monthCount: 1, year: 2018 },
       {  count: 165, monthCount: 2, year: 2018 },
       {  count: 103, monthCount: 3, year: 2018 },
       {  count: 60, monthCount: 4, year: 2018 }
    ]
    const data2 = [
      { count: 100, monthCount: 1, year: 2019 },
      {  count: 55, monthCount: 2, year: 2019 },
      {  count: 99, monthCount: 3, year: 2019 },
      {  count: 130, monthCount: 4, year: 2019 }
    ] 

我想获取 data3，它是 data2 - data1 及其 key 预期输出看起来像这样

[
    {count: 56, monthCount: 1 },
    {count: 100, monthCount: 2 },
    {count: 60, monthCount: 3 },
    {count: 70, monthCount: 4 }
]

Answer 1

如果您想减去data2 - data1，那么您可以通过vanilla JavaScript 来完成。让我举个例子。您的数据:

const data1 = [
  { count: 156, monthCount: 1, year: 2018 },
  {  count: 165, monthCount: 2, year: 2018 },
  {  count: 103, monthCount: 3, year: 2018 },
  {  count: 60, monthCount: 4, year: 2018 }
];
const data2 = [
 { count: 100, monthCount: 1, year: 2019 },
 {  count: 55, monthCount: 2, year: 2019 },
 {  count: 99, monthCount: 3, year: 2019 },
 {  count: 130, monthCount: 4, year: 2019 }
];

一个例子:

const combined = data1.concat(data2);
console.log(`combined, not calculated`, combined);

const desired = [...combined.reduce((r, {monthCount, count}) => {
const key = monthCount;

  const item = r.get(key) || Object.assign({}, {
    count: 0,
    monthCount: monthCount
  });

  if (item.count === 0)
    item.count = -count;
  else
    item.count += +count;

  return r.set(key, item);
}, new Map).values()];

console.log(`desired: `, desired)

输出:

[
    {count: -56, monthCount: 1},
    {count: -110, monthCount: 2},
    {count: -4, monthCount: 3},
    {count: 70, monthCount: 4},
]