Compare 2 arrays which returns difference

What's the fastest/best way to compare two arrays and return the difference? Much like array_diff in PHP. Is there an easy function or am I going to have to create one via each()? or a foreach loop?

I know this is an old question, but I thought I would share this little trick.

var diff = $(old_array).not(new_array).get();

diff now contains what was in old_array that is not in new_array

Working demo http://jsfiddle.net/u9xES/

Good link (Jquery Documentation): http://docs.jquery.com/Main_Page {you can search or read APIs here}

Hope this will help you if you are looking to do it in JQuery.

The alert in the end prompts the array of uncommon element Array i.e. difference between 2 array.

Please lemme know if I missed anything, cheers!

Code

var array1 = [1, 2, 3, 4, 5, 6];
var array2 = [1, 2, 3, 4, 5, 6, 7, 8, 9];
var difference = [];

jQuery.grep(array2, function(el) {
        if (jQuery.inArray(el, array1) == -1) difference.push(el);
});

alert(" the difference is " + difference);​ // Changed variable name 

use underscore as :

_.difference(array1,array2)

var arrayDiff = function (firstArr, secondArr) {
    var i, o = [], fLen = firstArr.length, sLen = secondArr.length, len;
    
    
    if (fLen > sLen) {
        len = sLen;
    } else if (fLen < sLen) {
        len = fLen;
    } else {
        len = sLen;
    }
    for (i=0; i < len; i++) {
        if (firstArr[i] !== secondArr[i]) {
            o.push({idx: i, elem1: firstArr[i], elem2: secondArr[i]});  //idx: array index
        }
    }
    
    if (fLen > sLen) {  // first > second
        for (i=sLen; i< fLen; i++) {
            o.push({idx: i, 0: firstArr[i], 1: undefined});
        }
    } else if (fLen < sLen) {
        for (i=fLen; i< sLen; i++) {
            o.push({idx: i, 0: undefined, 1: secondArr[i]});
        }
    }    
    
    return o;
};

/** SUBTRACT ARRAYS **/
function subtractarrays(array1, array2){
	var difference = [];
	for( var i = 0; i < array1.length; i++ ) {
		if( $.inArray( array1[i], array2 ) == -1 ) {
					difference.push(array1[i]);
		}
	}

	return difference;
}	

You can then call the function anywhere in your code.

var I_like    = ["love", "sex", "food"];
var she_likes = ["love", "food"];

alert( "what I like and she does't like is: " + subtractarrays( I_like, she_likes ) ); //returns "Naughty"!

This works in all cases and avoids the problems in the methods above. Hope that helps!

if you also want to compare the order of the answer you can extend the answer to something like this:

Array.prototype.compareTo = function (array2){
    var array1 = this;
    var difference = [];
    $.grep(array2, function(el) {
        if ($.inArray(el, array1) == -1) difference.push(el);
    });
    if( difference.length === 0 ){
        var $i = 0;
        while($i < array1.length){
            if(array1[$i] !== array2[$i]){
                return false;
            }
            $i++;
        }
        return true;
    }
    return false;
}

In this way you don't need to worry about if the first array is smaller than the second one.

var arr1 = [1, 2, 3, 4, 5, 6,10],
    arr2 = [1, 2, 3, 4, 5, 6, 7, 8, 9];
		
function array_diff(array1, array2){
	var difference = $.grep(array1, function(el) { return $.inArray(el,array2) < 0});
	return difference.concat($.grep(array2, function(el) { return $.inArray(el,array1) < 0}));;
}

console.log(array_diff(arr1, arr2));

The short version can be like this:

const diff = (a, b) => b.filter((i) => a.indexOf(i) === -1);

result:

diff(['a', 'b'], ['a', 'b', 'c', 'd']);

["c", "d"]

Array operations like this is not jQuery's strongest point. You should consider a library such as Underscorejs, specifically the difference function.

This should work with unsorted arrays, double values and different orders and length, while giving you the filtered values form array1, array2, or both.

function arrayDiff(arr1, arr2) {
    var diff = {};

    diff.arr1 = arr1.filter(function(value) {
        if (arr2.indexOf(value) === -1) {
            return value;
        }
    });

    diff.arr2 = arr2.filter(function(value) {
        if (arr1.indexOf(value) === -1) {
            return value;
        }
    });

    diff.concat = diff.arr1.concat(diff.arr2);

    return diff;
};

var firstArray = [1,2,3,4];
var secondArray = [4,6,1,4];

console.log( arrayDiff(firstArray, secondArray) );
console.log( arrayDiff(firstArray, secondArray).arr1 );
// => [ 2, 3 ]
console.log( arrayDiff(firstArray, secondArray).concat );
// => [ 2, 3, 6 ]