通过键减少转换单个数组答案

【问题标题】：Transform single an array with reduce by key通过键减少转换单个数组
【发布时间】：2021-12-30 04:17:03
【问题描述】：

我在这里Transform an Array into an Object using .reduce() 提出了类似的问题，但是我正在尝试使用 findIndex 找到替代解决方案。

这个输入数据：

const reports = [
  {
    dateOfReport: "11-01-2021",
    userId: "id1",
    userMetric: { first_metric: 10, second_metric: 15 },
  },
  {
    dateOfReport: "11-01-2021",
    userId: "id2",
    userMetric: { first_metric: 9, second_metric: 14 },
  },
  {
    dateOfReport: "12-01-2021",
    userId: "id1",
    userMetric: { first_metric: 11, second_metric: 14 },
  },
  {
    dateOfReport: "12-01-2021",
    userId: "id2",
    userMetric: { first_metric: 16, second_metric: 19 },
  },
];

输出数据必须是：

const output = [
  {
    dateOfReport: "11-01-2021",
    id1: { first_metric: 10, second_metric: 15 },
    id2: { first_metric: 9, second_metric: 14 },
  },
  {
    dateOfReport: "12-01-2021",
    id1: { first_metric: 11, second_metric: 14 },
    id2: { first_metric: 16, second_metric: 19 },
  },
];

我尝试在下面编写类似的代码，但输出中出现重复数据。谁能帮忙解决这个问题？

const groupedReports = reports.reduce((acc, dataItem) => {
    const nodeIndex = acc.findIndex((item) => item.dateOfReport === dataItem.dateOfReport);
    const newNode = { date: dataItem.date, [dataItem.userId]: dataItem.userMetric };

    console.log("NEW NODE", newNode);

    return [...acc.slice(0, nodeIndex - 1), newNode, ...acc.slice(nodeIndex + 1)]
  }, []);

【问题讨论】：

标签： javascript arrays reduce

【解决方案1】：

您可以使用一个对象进行分组并将新属性分配给 id。

const
    reports = [{ dateOfReport: "11-01-2021", userId: "id1", userMetric: { first_metric: 10, second_metric: 15 } }, { dateOfReport: "11-01-2021", userId: "id2", userMetric: { first_metric: 9, second_metric: 14 } }, { dateOfReport: "12-01-2021", userId: "id1", userMetric: { first_metric: 11, second_metric: 14 } }, { dateOfReport: "12-01-2021", userId: "id2", userMetric: { first_metric: 16, second_metric: 19 } }],
    result = Object.values(reports.reduce((r, { dateOfReport, userId, userMetric }) => {
        (r[dateOfReport] ??= { dateOfReport })[userId] = userMetric;
        return r;
    }, {}));

console.log(result);

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【讨论】：

//(r[dateOfReport] ??= { dateOfReport })[userId] = userMetric;据我了解，此解决方案会改变对象而不是创建新对象
这个属性赋值有什么问题？

【解决方案2】：

我认为你可以这样做：

reports.reduce((pre, cur) => {
    let index = pre.findIndex(item => item.dateOfReport == cur.dateOfReport)
    if (index != -1) {
        pre[index][cur.userId] = cur.userMetric
    } else {
        pre.push({
            dateOfReport: cur.dateOfReport,
            [cur.userId]: cur.userMetric
        })
    }
    return pre
}, [])

【讨论】：

我注意到你的代码使用了slice，它消耗了太多的性能。

【解决方案3】：

这是我的解决方案：

const reports = [
  {
    dateOfReport: "11-01-2021",
    userId: "id1",
    userMetric: { first_metric: 10, second_metric: 15 },
  },
  {
    dateOfReport: "11-01-2021",
    userId: "id2",
    userMetric: { first_metric: 9, second_metric: 14 },
  },
  {
    dateOfReport: "12-01-2021",
    userId: "id1",
    userMetric: { first_metric: 11, second_metric: 14 },
  },
  {
    dateOfReport: "12-01-2021",
    userId: "id2",
    userMetric: { first_metric: 16, second_metric: 19 },
  },
];

const sortReports = (reports) => {
    // Array of dates with no duplicates
    const dates = [...new Set(reports.map(el => el.dateOfReport))];
    // Replace each date with an array of reports that are relevant to the date
    // Reduce each array of reports into an object with your desired format
    const newReports = dates
      .map(date => reports
      .filter(report => report.dateOfReport === date)
      .reduce(el => ({
        dateOfReport: el.dateOfReport,
        [el.userId]: el.userMetric
      })));
    return newReports;
}
  
console.log(sortReports(reports));

【讨论】：