Transform single an array with reduce by key

Question

I asked a similar question here Transform an Array into an Object using .reduce(), however I am trying to find an alternative solution with findIndex.

This input data:

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 },
  },
];

Output data must be:

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 },
  },
];

I tried to write similar code below, but I get duplicate data in the output. Can anyone help solve this problem?

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)]
  }, []);

score 1 · Answer 1 · answered Nov 19 '21 at 11:30

1

I think your can do like this:

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
}, [])

answered Nov 19 '21 at 11:30

peter roe

21
6

I notice your code use `slice` , It consume too much performance. – peter roe Nov 19 '21 at 11:31

score 1 · Accepted Answer · answered Nov 19 '21 at 11:52

You could take an object for grouping and assign the new properties to the 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);

.as-console-wrapper { max-height: 100% !important; top: 0; }

//(r[dateOfReport] ??= { dateOfReport })[userId] = userMetric; As I understand it, this solution mutates the object rather than creating a new one — No Name, Nov 19 '21 at 13:25

score 0 · Answer 3 · answered Nov 19 '21 at 11:52

Here's my solution:

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));

Transform single an array with reduce by key

3 Answers3