How to concat two arrays and remove duplicates in javascript

Question

I want concat following two arrays by removing duplicates without assigning to third variable:

var arr1=[{id:1,name:'AB'},{id:2,name:'CD'}];

var arr2=[{id:3,name:'EF'},{id:2,name:'CD'}];

I want arr1 like:

[{id:1,name:'AB'},{id:2,name:'CD'},{id:3,name:'EF'}]

arr1.concat(arr2);

Use lodash union https://lodash.com/docs/4.17.10#union or https://lodash.com/docs/4.17.11#uniqWith — CornelC, Jan 08 '19 at 10:56
you can simply loop through array which has less elements & compare with the other array . push the non-existing object to the same array to avoid usage 3rd variable.. — super cool, Jan 08 '19 at 11:09
`$.each(arr1,(i,x)=>{ if($.grep(arr2,(y)=> x.id == y.id && x.name==y.name ).length < 1) arr2.push(x); });` something like this, hope if helps. you can use `.filter` inplace of grep in `ang` — super cool, Jan 08 '19 at 11:53
I posted [here](https://stackoverflow.com/a/60918864/4934446) an option with `JSON.stringify` — Jöcker, Mar 29 '20 at 18:26

score 7 · Answer 1 · answered Jan 08 '19 at 11:09

First merge two arrays then put array into a map with their ids. Then create array from map values.

var arr1=[{id:1,name:'AB'},{id:2,name:'CD'}];
var arr2=[{id:3,name:'EF'},{id:2,name:'CD'}];

arr1 = arr1.concat(arr2) // merge two arrays
let foo = new Map();
for(const tag of arr1) {
  foo.set(tag.id, tag);
}
let final = [...foo.values()]
console.log(final)

Ashish Ranjan · Answer 2 · 2019-01-08T11:01:06.353

6

Can use Array reduce and findIndex to achieve what you want.

var arr1=[{id:1,name:'AB'},{id:2,name:'CD'}];

var arr2=[{id:3,name:'EF'},{id:2,name:'CD'}];

// loop over arr2, add the elements of array2 if it doesn't exist in array1
var newArr = arr2.reduce((acc, eachArr2Elem) => {
  if (arr1.findIndex((eachArr1Elem) => eachArr1Elem.id === eachArr2Elem.id && eachArr1Elem.name === eachArr2Elem.name)  === -1) {
    acc.push(eachArr2Elem)
  }
  return acc
}, [...arr1]); // initialize the new Array with the contents of array1

console.log(newArr)

edited Jan 08 '19 at 11:01

answered Jan 08 '19 at 10:57

Ashish Ranjan

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is it possible without assigning to third variable – madhu Goud Jan 08 '19 at 11:00
@madhuGoud: You also mean the variables in the callBacks? I guess No (Not in plain Javascript), Here the elements are `Objects`, there is no simple way to concat them and remove duplicates – Ashish Ranjan Jan 08 '19 at 11:02
is it possible in typescript – madhu Goud Jan 08 '19 at 11:16
@madhuGoud: TypeScript is just a superset of Javascript, it is not a library. I am not clear with what you mean by the third variable. Do you want to modify any of the existing `arr1` or `arr2` with new array? Remember, something like: `arr1.concat(arr2);` is also a new reference, its just that you are not assigning it to a variable – Ashish Ranjan Jan 08 '19 at 11:18
@madhuGoud Check my solution if you want, I solved this with using map. Since your arrays have objects in it, it's not that simple. If your arrays were not objects, you could use `Set` to achieve unique array easily. – westdabestdb Jan 08 '19 at 11:19

score 1 · Answer 3 · answered Jan 08 '19 at 12:00

using the spread operator you can flatten any amount of arrays passed to the combineAndDeDup method, i have also split out some logic methods for (hopefully) more readable code. i hope this helps.

const arr1 = [{id:1,name:'AB'}, {id:2,name:'CD'}]
const arr2 = [{id:3,name:'EF'}, {id:2,name:'CD'}]

const flatten = a => [].concat.apply([], a)
const noDuplicateProps = (a, b) => Object.keys(a).some(k => a[k] === b[k])

const combineAndDeDup = (...arrs) => {
  
  return flatten(arrs).reduce((acc, item) => {
    const uniqueItem = acc.findIndex(i => noDuplicateProps(i, item)) === -1
    
    if (uniqueItem) return acc.concat([ item ])
    
    return acc
  }, [])
}


const deDuped = combineAndDeDup(arr1, arr2)
const megaDeDuped = combineAndDeDup(arr1, arr2, arr1, arr1, arr2, arr1)

console.log(deDuped)
console.log(megaDeDuped)

what to add if in case one array is empty than the result should be empty as well? — dorcsi, Oct 05 '21 at 15:31

score 1 · Answer 4 · answered Mar 16 '22 at 05:10

If you like clean ES6 try this:
Happy code :)

function arrayWithNoDuplicates(array, field) {
  const arrayWithoutNoDuplicates = array.filter((value, index, self) =>
    index === self.findIndex((t) => (
      t[field] === value[field]
    ))
  )
  return arrayWithoutNoDuplicates
}

const arr1 = [{id:1,name:'AB'}, {id:2,name:'CD'}]
const arr2 = [{id:3,name:'EF'}, {id:2,name:'CD'}]

// The first param is the two merged arrays and the second the field you
// to filter by
console.log(arrayWithNoDuplicates([...arr1, ...arr2], 'id'))

score 0 · Answer 5 · answered Jan 08 '19 at 11:02

0

By using lodash _.uniqWith(array, [comparator])

var objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }, { 'x': 1, 'y': 2 }];

_.uniqWith(objects, _.isEqual);
// => [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }]

answered Jan 08 '19 at 11:02

CornelC

4,974
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score 0 · Answer 6 · answered Jan 08 '19 at 12:04

  var arr1 = [{ id: 1, name: 'AB' }, { id: 2, name: 'CD' }];
  var arr2 = [{ id: 3, name: 'EF' }, { id: 3, name: 'XX' }];
  arr1.forEach(element => {
    arr2.forEach((el, idx) => {
      if (element.id === el.id || element.name === el.name) {
        delete arr2[idx]
      }
    });
  });

  let data = arr1.concat(arr2)

  // or arr1 = arr1.concat(arr2)
  // then your arr1 contains your unique array

data variable contains your unique array

score 0 · Answer 7 · answered Dec 12 '21 at 19:03

Here is the one liner that compares by id.

let result = arr1.concat( arr2.filter( i2 => !arr1.find( i1 => i1.id == i2.id ) ) );

I have modified elements to show what happens for different objects with the same id. Swap arr1 with arr2 for which array you want to keep your preferred components. There seems to be no simple way to compare objects in JavaScript, you may use JSON.stringify but that depends on elements order. You can try it out at https://playcode.io/new/ :

var arr1=[{id:1,name:'AB'},{id:2,name:'CD'}];
var arr2=[{id:3,name:'EF'},{id:2,name:'GH'}];

let result;

result = arr1.concat( arr2.filter( i2 => !arr1.find( i1 => i1.id == i2.id ) ) );

console.log('RESULT: ' + JSON.stringify(result));

result = arr1.concat(
  arr2.filter(
    i2 => !arr1.find(
      i1 => {
        console.log('I1: ' + JSON.stringify(i1) + ' I2: ' + JSON.stringify(i2));
        return i1.id == i2.id;}
        )
  )
);

console.log('RESULT: ' + JSON.stringify(result));

result = arr2.concat(
  arr1.filter(
    i1 => !arr2.find(
      i2 => {
        console.log('I1: ' + JSON.stringify(i1) + ' I2: ' + JSON.stringify(i2));
        return i1.id == i2.id;}
        )
  )
);

console.log('RESULT: ' + JSON.stringify(result));

score 0 · Answer 8 · answered Feb 16 '23 at 03:18

Both lodash function unionBy and unionWith can solve your problem.

If your objects has unique key, unionBy is the most elegant way to handle it.

var arr1 = [{id:1,name:'AB'},{id:2,name:'CD'}];
var arr2 = [{id:3,name:'EF'},{id:2,name:'CD'}];
var mergedWithoutDups = _.unionBy(arr1, arr2. 'id')

If your object has no unique key, use unionWith and isEqual instead. This will take deep comparison on all objects to remove duplicate.

var arr1 = [{id:1,name:'AB'},{id:2,name:'CD'}];
var arr2 = [{id:3,name:'EF'},{id:2,name:'CD'}];
var mergedWithoutDups = _.unionWith(arr1, arr2. _.isEqual)

How to concat two arrays and remove duplicates in javascript

8 Answers8