Javascript: Return first duplicate from array of objects based on object first index value

Question

I need to create a function to only display duplicate data from the first object that is a duplicate. If you look in my code I have an array with objects inside of it. My data structure is like this:

[
 { data: ["22409972", "1267304", "1000", "FG-18-1267304"] },
 { data: ["22409972", "1267304", "2000", "FG-18-1267304"] }
]

In this scenario I would not want to include the second object of data since its first index already exists in the first object "22409972"

I need a solution that could support having multiple duplicate objects with the same first index, still only wanting to return the first object containing the duplicate index

Essentially if a duplicate object exists remove it from the arrayThatContainsDuplicates array

I tried to use this as a solution

 const noDuplicates = [];
    for (let i = 0; i < duplicateRows.length; i++) {
      if (i + 1 < duplicateRows.length) {
        if (duplicateRows[i].data[0] !== duplicateRows[i + 1].data[0]) {
          noDuplicates.push(duplicateRows[i]);
        }
      }

The issue with this code is the duplicates are still being returned in the noDuplicates array

General Poxter · Accepted Answer · 2020-10-27 01:51:05Z

1

The problem with your code is that it's only comparing the current object to the next object. A duplicate of the current object could lie anywhere in the array, and your code does not take that into account.

Use this instead:

let firstElements = [];
let noDuplicates = [];
duplicateRows.forEach(object => {
    if (!firstElements.includes(object.data[0])) {
        firstElements.push(object.data[0]);
        noDuplicates.push(object);
    }
});

answered Oct 27, 2020 at 1:51

General Poxter

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Comments

kiranvj · Accepted Answer · 2020-10-27 02:02:19Z

A different approach.

Iterate the array, and create an object. Since object keys are unique, it will replace if there is a duplicate. You can also add a check if a key is already there, in that case don't update it again.

let list = [{
    data: ["22409972", "1267304", "1000", "FG-18-1267304"]
  },
  {
    data: ["22409972", "1267304", "2000", "FG-18-1267304"]
  },
  {
    data: ["22409979", "1267304", "2000", "FG-18-1267304"]
  },
  {
    data: ["224099720", "1267304", "2000", "FG-18-1267304"]
  },
  {
    data: ["224099728", "1267304", "2000", "FG-18-1267304"]
  },
  {
    data: ["224099728", "1267304", "2000", "FG-18-1267304"]
  }
];


let result = {};

list.forEach(item => {
  result[item.data[0]] = item;
});

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

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