Get list of duplicate objects in an array based on two property in javascript

Question

I am trying to get duplicate objects within an array based on 2 properties. Let's say the object is like below.

let arry = [
    {Level: "A-1", Status: "approved"},
    {Level: "A-2", Status: "approved"},
    {Level: "A-3", Status: "approved"},
    {Level: "A-4", Status: "reject"},
    {Level: "A-5", Status: "reject"},
    {Level: "A-1", Status: "approved"},
    {Level: "A-2", Status: "approved"},
    {Level: "A-6", Status: "approved"},
    {Level: "A-7", Status: "reject"},
    {Level: "A-1", Status: "approved"},
    {Level: "A-6", Status: "approved"},
]

Duplicate objects should return and only the Status "approved" once like below:

[
{Level: "A-1", Status: "approved"},
 {Level: "A-2", Status: "approved"}
]

"I am trying..." - So, what have you tried so far to solve this on your own? — Andreas
– Andreas, Commented Sep 9, 2020 at 17:42
Does this answer your question? Get list of duplicate objects in an array of objects — Heretic Monkey
– Heretic Monkey, Commented Sep 9, 2020 at 20:08

GirkovArpa · Accepted Answer · 2020-09-09 19:46:16Z

You can use Array.reduce to keep track of all the previous items as it iterates through the array, while preserving only the ones it's seen before (whose Status is "approved").

In order to not output duplicates of duplicates, it also checks if the current duplicate was already found as a duplicate, and ignores it if so.

const array = [
  { Level: "A-1", Status: "approved" },
  { Level: "A-2", Status: "approved" },
  { Level: "A-3", Status: "approved" },
  { Level: "A-4", Status: "reject" },
  { Level: "A-5", Status: "reject" },
  { Level: "A-1", Status: "approved" },
  { Level: "A-2", Status: "approved" },
  { Level: "A-6", Status: "approved" },
  { Level: "A-7", Status: "reject" },
  { Level: "A-1", Status: "approved" },
  { Level: "A-6", Status: "approved" },
];

const dupes = array.reduce((dupes, { Level, Status }, i) => {
  const matches = ({ Level: l, Status: s }) => l == Level && s == Status;
  const match = dupes.memory.find(matches);
  const found = dupes.dupes.find(matches);
  (match?.Status == 'approved' && !found)
    ? dupes.dupes.push({ Level, Status })
    : dupes.memory.push({ Level, Status });
  return (i == array.length - 1) ? dupes.dupes : dupes;
}, { dupes: [], memory: [] });

console.log(dupes);

A less general but more terse strategy might be:

const dupes = [...new Set(array
  .filter(({ Status: s }) => s == 'approved')
  .map(({ Level: l }) => +l.match(/\d+/)[0])
  .filter((num, _, arr) => arr.filter((n) => n == num).length > 1))]
  .map((n) => ({ Level: 'A-' + n, Status: 'approved' }));

For example:

const array = [
  { Level: "A-1", Status: "approved" },
  { Level: "A-2", Status: "approved" },
  { Level: "A-3", Status: "approved" },
  { Level: "A-4", Status: "reject" },
  { Level: "A-5", Status: "reject" },
  { Level: "A-1", Status: "approved" },
  { Level: "A-2", Status: "approved" },
  { Level: "A-6", Status: "approved" },
  { Level: "A-7", Status: "reject" },
  { Level: "A-1", Status: "approved" },
  { Level: "A-6", Status: "approved" },
];

const dupes = [...new Set(array
  .filter(({ Status: s }) => s == 'approved')
  .map(({ Level: l }) => +l.match(/\d+/)[0])
  .filter((num, _, arr) => arr.filter((n) => n == num).length > 1))]
  .map((n) => ({ Level: 'A-' + n, Status: 'approved' }));

console.log(dupes);

Gorynych · Accepted Answer · 2020-09-09 20:03:13Z

let arry = [
    {Level: "A-1", Status: "approved"},
    {Level: "A-2", Status: "approved"},
    {Level: "A-3", Status: "approved"},
    {Level: "A-4", Status: "reject"},
    {Level: "A-5", Status: "reject"},
    {Level: "A-1", Status: "approved"},
    {Level: "A-2", Status: "approved"},
    {Level: "A-6", Status: "approved"},
    {Level: "A-7", Status: "reject"},
    {Level: "A-1", Status: "approved"},
    {Level: "A-6", Status: "approved"},
]

function dups(arry) {
  const hashMap = {};

  return arry.reduce((acc, curr) => {
    const level = curr.Level;
    if(hashMap[level] && hashMap[level] === 1 && curr.Status === 'approved') {
      acc.push(curr);
      hashMap[level]++;
    } else {
      hashMap[level] = 1;
    }

    return acc;
  }, []);
}

console.log(dups(arry));

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