Compare two Javascript Arrays and remove Duplicates

array1 = array1.filter(function(val) {
 return array2.indexOf(val) == -1;
});

Or, with the availability of ES6:

array1 = array1.filter(val => !array2.includes(val));

filter() reference here

indexOf() reference here

includes() reference here

The trick, for reasons that are beyond me, is to loop the outer loop downwards (i--) and the inner loop upwards (j++).

See the example bellow:

function test() {
 var array1 = new Array("a","b","c","d","e","f");
 var array2 = new Array("c","e");
 for (var i = array1.length - 1; i >= 0; i--) {
 for (var j = 0; j < array2.length; j++) {
 if (array1[i] === array2[j]) {
 array1.splice(i, 1);
 }
 }
 }
 console.log(array1)
 }

How do I know this? See the below:

for( var i =myArray.length - 1; i>=0; i--){
 for( var j=0; j<toRemove.length; j++){
 if(myArray[i] === toRemove[j]){
 myArray.splice(i, 1);
 }
 }
}

or

var myArray = [
 {name: 'deepak', place: 'bangalore'}, 
 {name: 'chirag', place: 'bangalore'}, 
 {name: 'alok', place: 'berhampur'}, 
 {name: 'chandan', place: 'mumbai'}
];
var toRemove = [
 {name: 'deepak', place: 'bangalore'},
 {name: 'alok', place: 'berhampur'}
];
for( var i=myArray.length - 1; i>=0; i--){
 for( var j=0; j<toRemove.length; j++){
 if(myArray[i] && (myArray[i].name === toRemove[j].name)){
 myArray.splice(i, 1);
 }
 }
}
alert(JSON.stringify(myArray));

On that note, would anyone be able to explain why the outer loop needs to be looped downwards (--)?

Good luck!

You can try this

array1 = array1 .filter(val => {
 return !array2.find((val2)=>{
 // console.log({valueID:val.id+":"+val2.id});
 return val.id===val2.id
 }) 
 });

Using the Set.prototype Constructor: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set

let array1 = Array('a', 'b', 'c', 'd', 'e', 'f')
let array2 = Array('c', 'e', 'g')
let concat = array1.concat(array2) // join arrays => [ 'a', 'b', 'c', 'd', 'e', 'f', 'c', 'e', 'g' ]
// Set will filter out duplicates automatically
let set = new Set(concat) // => Set { 'a', 'b', 'c', 'd', 'e', 'f', 'g' }
// Use spread operator to extend Set to an Array
let result = [...set]
console.log(result) // => [ 'a', 'b', 'c', 'd', 'e', 'f', 'g' ]

use Array.splice()

var array1 = ['1', '2', '3', '4', '5'];
var array2 = ['4', '5'];
var index;
for (var i=0; i<array2.length; i++) {
 index = array1.indexOf(array2[i]);
 if (index > -1) {
 array1.splice(index, 1);
 }
}

This is my solution to remove duplicate in ES6.

let foundDuplicate = false;
existingOptions.some(existingItem => {
 result = result.filter(item => {
 if (existingItem.value !== item.value) {
 return item;
 } else {
 foundDuplicate = true;
 }
 });
 return foundDuplicate;
});

I used this approach because in my case I was having array of objects and indexOf was having problem with it.

This my solution

array1 = array1.filter(function(val) { return array2.indexOf(val.toString()) == -1; });

window.onload = function () {
 var array1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm'];
 var array2 = ['c', 'h', 'k'];
 var array3 = [];
 var SecondarrayIndexcount = 0;
 for (var i = 0; i < array1.length; i++) {
 for (var j = 0; j < array2.length; j++) {
 if (array1[i] !== array2[j]) {
 if (SecondarrayIndexcount === (array2.length - 1)) {
 array3.push(array1[i]);
 SecondarrayIndexcount = 0;
 break;
 }
 SecondarrayIndexcount++;
 }
 }
 }
 for (var i in array3) {
 alert(array3[i]);
 }
 }
</script>

• javascript