准备报告数据时的功能性Java映射/减少

Question

我正在努力了解如何正确地使用Array.reduce()来汇总摘要/报告数据（即分组计数）。我通常通过用forEach遍历数据并构建对象来手动执行此操作，但是我觉得链接map和reduce必须成为一种更优雅，更实用的方法；我只是无法弄清楚如何正确执行此操作。

这是我的实验带给我的地方：

const articleData = [
    {newsSource: "AP", title: "Some article.", category: "World"},
    {newsSource: "BBC", title: "Some article.", category: "Politics"},
    {newsSource: "CBS", title: "Some article.", category: "Sports"},
    {newsSource: "CNN", title: "Some article.", category: "Finance"},
    {newsSource: "CNN", title: "Another article.", category: "Politics"},
    {newsSource: "NBC", title: "Some article.", category: "Politics"},
    {newsSource: "NBC", title: "Another article.", category: "Finance"},
    {newsSource: "Reuters", title: "Some article.", category: "World"},
    {newsSource: "Reuters", title: "Another article.", category: "Politics"},
    {newsSource: "Reuters", title: "Yet another article.", category: "Finance"}
];

// I want to set reportData to be the result of the chained map/reduce
// ...not declare it here and assemble it within the functions below
let reportData = {};

articleData.map((item, index) => {
    if (item.newsSource) return item.newsSource;
})
.reduce((acc, newsSource) => {

    if (!reportData[newsSource]) {
        reportData[newsSource] = 1;
    } else {
        reportData[newsSource] = reportData[newsSource] + 1;
    }

    return (acc, reportData);

});

console.log(reportData);
// Expected output:
// { AP: 1, BBC: 1, CBS: 1, CNN: 2, NBC: 2, Reuters: 3 }

这里有很多问题。 （最重要的是它跳过了第一个数据元素！我认为我理解为什么，但是我不知道如何解决它。）但是最重要的是，我想了解如何构造我的[ C0]函数，因此我不更改其中的reduce，而是返回“预期输出”下显示的正确结构化的数据。

减少平面阵列对我来说很明显，但是一旦我处理了超出该深度的任何结构，我都会感到困惑。

Answer 1

您可以直接在reportData上使用Array.reduce：

Array.reduce

articleData

Answer 2

您可以通过拳头值在

reportData = articleData.reduce(function(c, a) {
  c[a.newsSource] = (c[a.newsSource] || 0) + 1;
  return c;
}, {});

console.log(reportData);

方法的

const articleData = [{
    newsSource: "AP",
    title: "Some article.",
    category: "World"
  },
  {
    newsSource: "BBC",
    title: "Some article.",
    category: "Politics"
  },
  {
    newsSource: "CBS",
    title: "Some article.",
    category: "Sports"
  },
  {
    newsSource: "CNN",
    title: "Some article.",
    category: "Finance"
  },
  {
    newsSource: "CNN",
    title: "Another article.",
    category: "Politics"
  },
  {
    newsSource: "NBC",
    title: "Some article.",
    category: "Politics"
  },
  {
    newsSource: "NBC",
    title: "Another article.",
    category: "Finance"
  },
  {
    newsSource: "Reuters",
    title: "Some article.",
    category: "World"
  },
  {
    newsSource: "Reuters",
    title: "Another article.",
    category: "Politics"
  },
  {
    newsSource: "Reuters",
    title: "Yet another article.",
    category: "Finance"
  }
];

reportData = articleData.reduce(function(c, a) {
  c[a.newsSource] = (c[a.newsSource] || 0) + 1;
  return c;
}, {});

console.log(reportData);

中累积。您可以在2nd param功能中跳过值或reduce值。

manipulate