将数组中的值分组并计数到对象中答案

【问题标题】：Group and count values in an array into an object将数组中的值分组并计数到对象中
【发布时间】：2021-06-05 21:16:11
【问题描述】：

我有以下数组形式的信息

0: { first: "sea",      second: "deniz",   languageId: "English-Turkish"}
1: { first: "play",     second: "oynamak", languageId: "English-Turkish"}
2: { first: "swim",     second: "yuzmek",  languageId: "English-Turkish"}
3: { first: "foo",      second: "bar",     languageId: "German-Russian"}
4: { first: "computer", second: "l'ordi",  languageId: "English-French"}

我需要将它们按languageId 分组并计算属于这些组的项目。为此，我还有以下对象，

export class stats{
    name: String;
    count: number;
}

最后我需要以下信息；

0: { name: "English-Turkish",  count: 3 }
1: { name: "German-Russian",   count: 1 }
2: { name: "English-French",   count: 1 }

Array.reduce 函数对我来说似乎是一个很好的方法，但无法弄清楚。我该如何实现？

【问题讨论】：

标签： javascript arrays typescript sorting group-by

【解决方案1】：

遗憾的是，array.reduce 可能不是解决此问题的正确工具。

但这就是你要找的吗？如果你需要经常使用它，你可以把它变成一个函数。

let items = [
  { first: "sea",      second: "deniz",   languageId: "English-Turkish"},
  { first: "play",     second: "oynamak", languageId: "English-Turkish"},
  { first: "swim",     second: "yuzmek",  languageId: "English-Turkish"},
  { first: "foo",      second: "bar",     languageId: "German-Russian"},
  { first: "computer", second: "l'ordi",  languageId: "English-French"},
];
let grouped = {};
for (let item of items) {
  let { languageId } = item;
  if (!(languageId in grouped)) {
    grouped[languageId] = [];
  }
  grouped[languageId].push(item);
}
let counts = Object.entries(grouped).map(([name, arr]) => ({ name, count: arr.length }));
console.log(counts);

这有grouped 和counts，所以如果你需要将它们全部组合在一起；它也有。

【讨论】：

【解决方案2】：

Array.reduce 函数对我来说似乎是一个很好的方法，但是想不通。我该如何实现？

您可以使用.reduce() 以更优雅的方式获得您的期望值，如下所示：

const items = [
  { first: "sea",      second: "deniz",   languageId: "English-Turkish"},
  { first: "play",     second: "oynamak", languageId: "English-Turkish"},
  { first: "swim",     second: "yuzmek",  languageId: "English-Turkish"},
  { first: "foo",      second: "bar",     languageId: "German-Russian"},
  { first: "computer", second: "l'ordi",  languageId: "English-French"},
];

const result = items.reduce((acc, {languageId}) => 
{
  acc[languageId] = acc[languageId] || {name: languageId, count: 0};
  // The more elegant way: acc[languageId] ??= {name: languageId, count: 0};
  acc[languageId]['count'] += 1;
  
  return acc;
}, {});

console.log(Object.values(result));

reduce() 方法在数组的每个元素，产生一个输出值。

【讨论】：