减少对象数组并返回对象的所有原始属性答案

【问题标题】：Reduce an array of objects and return all the original properties of the object减少对象数组并返回对象的所有原始属性
【发布时间】：2019-03-19 06:24:17
【问题描述】：

我有一个对象数组，每个对象有 4 个属性，如下所示：

let arr = [
{name: john, lastName: smith, counter:1, city: New York}
{name: john, lastName: smith, counter:1, city: New York}
{name: emilio, lastName: kouri, counter:1, city: euy}
{name: john, lastName: smith, counter:1, city: New York}
]

我想减少它以使其返回（总和）

[{name: emilio, lastName: kouri, counter:1, city: euy}
{name: john, lastName: smith, counter:3, city: New York}]

这是我现在使用的代码，它正确地减少了它但只返回[计数器，名称]，我希望它返回每个对象的所有四个属性，怎么做？

  let counts = arr.reduce((prev, curr) => {
    let count = prev.get(curr.name) || 0;

      prev.set(curr.name, curr.counter + count);
        return prev;
    }, new Map());


      let reducedObjArr = [...counts].map(([key, value]) => {
        return {key, value}
      })
    console.log('reducido',reducedObjArr);

【问题讨论】：

标签： javascript reduce

【解决方案1】：

您只需要一个 reduce 语句，没有嵌套的 map 语句：

let arr = [{
  name: "john",
  lastName: "smith",
  counter: 1,
  city: "New York"
}, {
  name: "john",
  lastName: "smith",
  counter: 1,
  city: "New York"
}, {
  name: "emilio",
  lastName: "kouri",
  counter: 1,
  city: "euy"
}, {
  name: "john",
  lastName: "smith",
  counter: 1,
  city: "New York"
}];

let counts = arr.reduce((acc, curr) => {
  if (!acc.some(({ name }) => name == curr.name)) {
    acc.push(curr);
  } else {
    acc.find(({ name }) => name == curr.name).counter++;
  }
  return acc;
}, []);

console.log(counts);

【讨论】：

没问题@SvenBrodersen。

【解决方案2】：

您可以获取计数为零的对象的副本，然后递增该对象并设置该对象。

let arr = [{ name: 'john', lastName: 'smith', counter: 1, city: 'New York' }, { name: 'john', lastName: 'smith', counter: 1, city: 'New York' }, { name: 'emilio', lastName: 'kouri', counter: 1, city: 'euy' }, { name: 'john', lastName: 'smith', counter: 1, city: 'New York' }];

let counts = arr.reduce((prev, curr) => {
    let item = prev.get(curr.name) || Object.assign({}, curr, { counter: 0 });
    item.counter += curr.counter;
    return prev.set(curr.name, item);
}, new Map);

let reducedObjArr = [...counts.values()]

console.log('reducido', reducedObjArr);

【讨论】：