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How to merge two arrays in JavaScript and de-duplicate items


Question

I have two JavaScript arrays:

var array1 = ["Vijendra","Singh"];
var array2 = ["Singh", "Shakya"];

I want the output to be:

var array3 = ["Vijendra","Singh","Shakya"];

The output array should have repeated words removed.

How do I merge two arrays in JavaScript so that I get only the unique items from each array in the same order they were inserted into the original arrays?

2017/10/18
1
1428
10/18/2017 6:29:39 AM

Accepted Answer

To just merge the arrays (without removing duplicates)

ES5 version use Array.concat:

var array1 = ["Vijendra", "Singh"];
var array2 = ["Singh", "Shakya"];

console.log(array1.concat(array2));

ES6 version use destructuring

const array1 = ["Vijendra","Singh"];
const array2 = ["Singh", "Shakya"];
const array3 = [...array1, ...array2];

Since there is no 'built in' way to remove duplicates (ECMA-262 actually has Array.forEach which would be great for this), we have to do it manually:

Array.prototype.unique = function() {
    var a = this.concat();
    for(var i=0; i<a.length; ++i) {
        for(var j=i+1; j<a.length; ++j) {
            if(a[i] === a[j])
                a.splice(j--, 1);
        }
    }

    return a;
};

Then, to use it:

var array1 = ["Vijendra","Singh"];
var array2 = ["Singh", "Shakya"];
// Merges both arrays and gets unique items
var array3 = array1.concat(array2).unique(); 

This will also preserve the order of the arrays (i.e, no sorting needed).

Since many people are annoyed about prototype augmentation of Array.prototype and for in loops, here is a less invasive way to use it:

function arrayUnique(array) {
    var a = array.concat();
    for(var i=0; i<a.length; ++i) {
        for(var j=i+1; j<a.length; ++j) {
            if(a[i] === a[j])
                a.splice(j--, 1);
        }
    }

    return a;
}

var array1 = ["Vijendra","Singh"];
var array2 = ["Singh", "Shakya"];
    // Merges both arrays and gets unique items
var array3 = arrayUnique(array1.concat(array2));

For those who are fortunate enough to work with browsers where ES5 is available, you can use Object.defineProperty like this:

Object.defineProperty(Array.prototype, 'unique', {
    enumerable: false,
    configurable: false,
    writable: false,
    value: function() {
        var a = this.concat();
        for(var i=0; i<a.length; ++i) {
            for(var j=i+1; j<a.length; ++j) {
                if(a[i] === a[j])
                    a.splice(j--, 1);
            }
        }

        return a;
    }
});
2020/06/20
1749
6/20/2020 9:12:55 AM

With Underscore.js or Lo-Dash you can do:

console.log(_.union([1, 2, 3], [101, 2, 1, 10], [2, 1]));
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>

http://underscorejs.org/#union

http://lodash.com/docs#union

2019/09/20

First concatenate the two arrays, next filter out only the unique items:

var a = [1, 2, 3], b = [101, 2, 1, 10]
var c = a.concat(b)
var d = c.filter((item, pos) => c.indexOf(item) === pos)

console.log(d) // d is [1, 2, 3, 101, 10]

Edit

As suggested a more performance wise solution would be to filter out the unique items in b before concatenating with a:

var a = [1, 2, 3], b = [101, 2, 1, 10]
var c = a.concat(b.filter((item) => a.indexOf(item) < 0))

console.log(c) // c is [1, 2, 3, 101, 10]

2019/09/20

This is an ECMAScript 6 solution using spread operator and array generics.

Currently it only works with Firefox, and possibly Internet Explorer Technical Preview.

But if you use Babel, you can have it now.

const input = [
  [1, 2, 3],
  [101, 2, 1, 10],
  [2, 1]
];
const mergeDedupe = (arr) => {
  return [...new Set([].concat(...arr))];
}

console.log('output', mergeDedupe(input));

2019/11/25

ES6

array1.push(...array2) // => don't remove duplication 

OR

[...array1,...array2] //   =>  don't remove duplication 

OR

[...new Set([...array1 ,...array2])]; //   => remove duplication
2016/11/17

Using a Set (ECMAScript 2015), it will be as simple as that:

const array1 = ["Vijendra", "Singh"];
const array2 = ["Singh", "Shakya"];
console.log(Array.from(new Set(array1.concat(array2))));

2019/11/25

Source: https://stackoverflow.com/questions/1584370
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