What is the best way to obtain a distinct collection from two arrays that eliminates the second appearance of an element based on a key's value, rather than the first as in the Lodash uniqueBy function?

Question

What is the best way to obtain a distinct collection from two arrays that eliminates the second appearance of an element based on a key's value, rather than the first as in the Lodash uniqueBy function?

Let's say I have two arrays...

const arr1 = [ { id: 1: newBid: true } ];

const arr2 = [ { id: 1, newBid: false }, { id: 2, newBid: false } ];

My goal is to end up with an array that looks like this

[ { id: 1, newBid: false }, { id: 2, newBid: false } ]

However, I specifically want the { id: 1, newBid: true } from arr1 and not arr2

I tried using Lodash uniqBy(arr1, arr2, ['id']), but it removes the first occurrence, not the second

javascript typescript lodash

Answer 1

Answer №1

For merging arrays in JavaScript, consider using the lodash library's mergeWith function.

const arr1 = [{
  id: 1,
  newBid: true
}];

const arr2 = [{
  id: 1,
  newBid: false
}, {
  id: 2,
  newBid: false
}];

function customizer(firstValue, secondValue) {
  if(firstValue) 
      return firstValue;
  else
      return secondValue;
}

console.log(_.mergeWith(arr1, arr2, customizer));

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.js"></script>

Answer 2

For merging arrays in JavaScript, consider using the lodash library's mergeWith function.

const arr1 = [{
  id: 1,
  newBid: true
}];

const arr2 = [{
  id: 1,
  newBid: false
}, {
  id: 2,
  newBid: false
}];

function customizer(firstValue, secondValue) {
  if(firstValue) 
      return firstValue;
  else
      return secondValue;
}

console.log(_.mergeWith(arr1, arr2, customizer));

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.js"></script>

Answer 3

Answer №2

When faced with these types of problems, I often opt to utilize an object as a map for convenience.

const arr1 = [ { id: 1, newBid: true } ];

const arr2 = [ { id: 1, newBid: false }, { id: 2, newBid: false } ];

const map = {};

function populateMap(array) {
    for(let i = 0; i < array.length; i++) {
        const item = array[i];
        map[item.id] = item;
    }
}

populateMap(arr1);
populateMap(arr2);

console.log(Object.values(map))

Answer 4

When faced with these types of problems, I often opt to utilize an object as a map for convenience.

const arr1 = [ { id: 1, newBid: true } ];

const arr2 = [ { id: 1, newBid: false }, { id: 2, newBid: false } ];

const map = {};

function populateMap(array) {
    for(let i = 0; i < array.length; i++) {
        const item = array[i];
        map[item.id] = item;
    }
}

populateMap(arr1);
populateMap(arr2);

console.log(Object.values(map))

What is the best way to obtain a distinct collection from two arrays that eliminates the second appearance of an element based on a key's value, rather than the first as in the Lodash uniqueBy function?

Answer №1

Answer №2

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