without - remove common elements from two arrays javascript




How to merge two arrays in JavaScript and de-duplicate items (20)

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?


DeDuplicate single or Merge and DeDuplicate multiple array inputs. Example below.

useing ES6 - Set, for of, destructuring

I wrote this simple function which takes multiple array arguments. Does pretty much the same as the solution above it just have more practical use case. This function doesn't concatenate duplicate values in to one array only so that it can delete them at some later stage.

SHORT FUNCTION DEFINITION ( only 9 lines )

/**
* This function merging only arrays unique values. It does not merges arrays in to array with duplicate values at any stage.
*
* @params ...args Function accept multiple array input (merges them to single array with no duplicates)
* it also can be used to filter duplicates in single array
*/
function arrayDeDuplicate(...args){
   let set = new Set(); // init Set object (available as of ES6)
   for(let arr of args){ // for of loops through values
      arr.map((value) => { // map adds each value to Set object
         set.add(value); // set.add method adds only unique values
      });
   }
   return [...set]; // destructuring set object back to array object
   // alternativly we culd use:  return Array.from(set);
}

USE EXAMPLE CODEPEN:

// SCENARIO 
let a = [1,2,3,4,5,6];
let b = [4,5,6,7,8,9,10,10,10];
let c = [43,23,1,2,3];
let d = ['a','b','c','d'];
let e = ['b','c','d','e'];

// USEAGE
let uniqueArrayAll = arrayDeDuplicate(a, b, c, d, e);
let uniqueArraySingle = arrayDeDuplicate(b);

// OUTPUT
console.log(uniqueArrayAll); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 43, 23, "a", "b", "c", "d", "e"]
console.log(uniqueArraySingle); // [4, 5, 6, 7, 8, 9, 10]

ES6

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

OR

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

OR

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

Assuming original arrays don't need de-duplication, this should be pretty fast, retain original order, and does not modify the original arrays...

function arrayMerge(base, addendum){
    var out = [].concat(base);
    for(var i=0,len=addendum.length;i<len;i++){
        if(base.indexOf(addendum[i])<0){
            out.push(addendum[i]);
        }
    }
    return out;
}

usage:

var array1 = ["Vijendra","Singh"];
var array2 = ["Singh", "Shakya"];
var array3 = arrayMerge(array1, array2);

console.log(array3);
//-> [ 'Vijendra', 'Singh', 'Shakya' ]

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(function (item, pos) {return c.indexOf(item) == pos});

// d is [1,2,3,101,10]

http://jsfiddle.net/simo/98622/

Edit

As suggested by @Dmitry (see the second comment below) 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(function (item) {
    return a.indexOf(item) < 0;
}));

// d is [1,2,3,101,10]

In Dojo 1.6+

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

dojo.forEach(array3, function(item) {
    if (dojo.indexOf(unique, item) > -1) return;
    unique.push(item); 
});

Update

See working code.

http://jsfiddle.net/UAxJa/1/


It can be done using Set.

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

var array3 = array1.concat(array2);
var tempSet = new Set(array3);
array3 = Array.from(tempSet);

//show output
document.body.querySelector("div").innerHTML = JSON.stringify(array3);
<div style="width:100%;height:4rem;line-height:4rem;background-color:steelblue;color:#DDD;text-align:center;font-family:Calibri" > 
  temp text 
</div>

Just throwing in my two cents.

function mergeStringArrays(a, b){
    var hash = {};
    var ret = [];

    for(var i=0; i < a.length; i++){
        var e = a[i];
        if (!hash[e]){
            hash[e] = true;
            ret.push(e);
        }
    }

    for(var i=0; i < b.length; i++){
        var e = b[i];
        if (!hash[e]){
            hash[e] = true;
            ret.push(e);
        }
    }

    return ret;
}

This is a method I use a lot, it uses an object as a hashlookup table to do the duplicate checking. Assuming that the hash is O(1), then this runs in O(n) where n is a.length + b.length. I honestly have no idea how the browser does the hash, but it performs well on many thousands of data points.


Merge an unlimited number of arrays or non-arrays and keep it unique:

function flatMerge() {
    return Array.prototype.reduce.call(arguments, function (result, current) {
        if (!(current instanceof Array)) {
            if (result.indexOf(current) === -1) {
                result.push(current);
            }
        } else {
            current.forEach(function (value) {
                console.log(value);
                if (result.indexOf(value) === -1) {
                    result.push(value);
                }
            });
        }
        return result;
    }, []);
}

flatMerge([1,2,3], 4, 4, [3, 2, 1, 5], [7, 6, 8, 9], 5, [4], 2, [3, 2, 5]);
// [1, 2, 3, 4, 5, 7, 6, 8, 9]

flatMerge([1,2,3], [3, 2, 1, 5], [7, 6, 8, 9]);
// [1, 2, 3, 5, 7, 6, 8, 9]

flatMerge(1, 3, 5, 7);
// [1, 3, 5, 7]

New solution ( which uses Array.prototype.indexOf and Array.prototype.concat ):

Array.prototype.uniqueMerge = function( a ) {
    for ( var nonDuplicates = [], i = 0, l = a.length; i<l; ++i ) {
        if ( this.indexOf( a[i] ) === -1 ) {
            nonDuplicates.push( a[i] );
        }
    }
    return this.concat( nonDuplicates )
};

Usage:

>>> ['Vijendra', 'Singh'].uniqueMerge(['Singh', 'Shakya'])
["Vijendra", "Singh", "Shakya"]

Array.prototype.indexOf ( for internet explorer ):

Array.prototype.indexOf = Array.prototype.indexOf || function(elt)
  {
    var len = this.length >>> 0;

    var from = Number(arguments[1]) || 0;
    from = (from < 0) ? Math.ceil(from): Math.floor(from); 
    if (from < 0)from += len;

    for (; from < len; from++)
    {
      if (from in this && this[from] === elt)return from;
    }
    return -1;
  };

Simplified simo's answer and turned it into a nice function.

function mergeUnique(arr1, arr2){
    return arr1.concat(arr2.filter(function (item) {
        return arr1.indexOf(item) === -1;
    }));
}

The easiest way to do this is either to use concat() to merge the arrays and then use filter() to remove the duplicates, or to use concat() and then put the merged array inside a Set().

First way:

const firstArray = [1,2, 2];
const secondArray = [3,4];
// now lets merge them
const mergedArray = firstArray.concat(secondArray); // [1,2,2,3,4]
//now use filter to remove dups
const removeDuplicates = mergedArray.filter((elem, index) =>  mergedArray.indexOf(elem) === index); // [1,2,3, 4]

Second way (but with performance implications on the UI):

const firstArray = [1,2, 2];
const secondArray = [3,4];
// now lets merge them
const mergedArray = firstArray.concat(secondArray); // [1,2,2,3,4]
const removeDuplicates = new Set(mergedArray);

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.

// Input: [ [1, 2, 3], [101, 2, 1, 10], [2, 1] ]
// Output: [1, 2, 3, 101, 10]
function mergeDedupe(arr)
{
  return [...new Set([].concat(...arr))];
}

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

const array1 = ["Vijendra", "Singh"];
const array2 = ["Singh", "Shakya"];
const array3 = Array.from(new Set(array1.concat(array2)));

Why don't you use an object? It looks like you're trying to model a set. This won't preserve the order, however.

var set1 = {"Vijendra":true, "Singh":true}
var set2 = {"Singh":true,  "Shakya":true}

// Merge second object into first
function merge(set1, set2){
  for (var key in set2){
    if (set2.hasOwnProperty(key))
      set1[key] = set2[key]
  }
  return set1
}

merge(set1, set2)

// Create set from array
function setify(array){
  var result = {}
  for (var item in array){
    if (array.hasOwnProperty(item))
      result[array[item]] = true
  }
  return result
}

You can achieve it simply using Underscore.js's => uniq:

array3 = _.uniq(array1.concat(array2))

console.log(array3)

It will print ["Vijendra", "Singh", "Shakya"].


You can do it simply with ECMAScript 6,

var array1 = ["Vijendra", "Singh"];
var array2 = ["Singh", "Shakya"];
var array3 = [...new Set([...array1 ,...array2])];
console.log(array3); // ["Vijendra", "Singh", "Shakya"];
  • Use the spread operator for concatenating the array.
  • Use Set for creating a distinct set of elements.
  • Again use the spread operator to convert the Set into an array.

looks like the accepted answer is the slowest in my tests;

note I am merging 2 arrays of objects by Key

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>
<button type='button' onclick='doit()'>do it</button>
<script>
function doit(){
    var items = [];
    var items2 = [];
    var itemskeys = {};
    for(var i = 0; i < 10000; i++){
        items.push({K:i, C:"123"});
        itemskeys[i] = i;
    }

    for(var i = 9000; i < 11000; i++){
        items2.push({K:i, C:"123"});
    }

    console.time('merge');
    var res = items.slice(0);

    //method1();
    method0();
    //method2();

    console.log(res.length);
    console.timeEnd('merge');

    function method0(){
        for(var i = 0; i < items2.length; i++){
            var isok = 1;
            var k = items2[i].K;
            if(itemskeys[k] == null){
                itemskeys[i] = res.length;
                res.push(items2[i]);
            }
        }
    }

    function method1(){
        for(var i = 0; i < items2.length; i++){
            var isok = 1;
            var k = items2[i].K;

            for(var j = 0; j < items.length; j++){
                if(items[j].K == k){
                    isok = 0;
                    break;
                }
            }

            if(isok) res.push(items2[i]);
        }  
    }

    function method2(){
        res = res.concat(items2);
        for(var i = 0; i < res.length; ++i) {
            for(var j = i+1; j < res.length; ++j) {
                if(res[i].K === res[j].K)
                    res.splice(j--, 1);
            }
        }
    }
}
</script>
</body>
</html>

merge two arrays and remove duplicate in es6

let arr1 = [3, 5, 2, 2, 5, 5];
let arr2 = [2, 1, 66, 5];
let unique = [...new Set([...arr1,...arr2])];
console.log(unique);
// [ 3, 5, 2, 1, 66 ]

Array.prototype.add = function(b){
    var a = this.concat();                // clone current object
    if(!b.push || !b.length) return a;    // if b is not an array, or empty, then return a unchanged
    if(!a.length) return b.concat();      // if original is empty, return b

    // go through all the elements of b
    for(var i = 0; i < b.length; i++){
        // if b's value is not in a, then add it
        if(a.indexOf(b[i]) == -1) a.push(b[i]);
    }
    return a;
}

// Example:
console.log([1,2,3].add([3, 4, 5])); // will output [1, 2, 3, 4, 5]

Array.prototype.merge = function(/* variable number of arrays */){
    for(var i = 0; i < arguments.length; i++){
        var array = arguments[i];
        for(var j = 0; j < array.length; j++){
            if(this.indexOf(array[j]) === -1) {
                this.push(array[j]);
            }
        }
    }
    return this;
};

A much better array merge function.





merge