Question

65

Finding matches between multiple JavaScript Arrays

rated 0 times [ 72] [ 7] / answers: 1 / hits: 74930 / 12 Years ago, mon, june 18, 2012, 12:00:00

I have multiple arrays with string values and I want to compare them and only keep the matching results that are identical between ALL of them.

Given this example code:

var arr1 = ['apple', 'orange', 'banana', 'pear', 'fish', 'pancake', 'taco', 'pizza'];

var arr2 = ['taco', 'fish', 'apple', 'pizza'];

var arr3 = ['banana', 'pizza', 'fish', 'apple'];

I would like to to produce the following array that contains matches from all given arrays:

['apple', 'fish', 'pizza']

I know I can combine all the arrays with var newArr = arr1.concat(arr2, arr3); but that just give me an array with everything, plus the duplicates. Can this be done easily without needing the overhead of libraries such as underscore.js?

(Great, and now i'm hungry too!)

EDIT I suppose I should mention that there could be an unknown amount of arrays, I was just using 3 as an example.

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mireyag

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answered 12 Years ago jarrettw · Accepted Answer

var result = arrays.shift().filter(function(v) {

    return arrays.every(function(a) {

        return a.indexOf(v) !== -1;

    });

});

DEMO: http://jsfiddle.net/nWjcp/2/

You could first sort the outer Array to get the shortest Array at the beginning...

arrays.sort(function(a, b) {

    return a.length - b.length;

});

For completeness, here's a solution that deals with duplicates in the Arrays. It uses .reduce() instead of .filter()...

var result = arrays.shift().reduce(function(res, v) {

    if (res.indexOf(v) === -1 && arrays.every(function(a) {

        return a.indexOf(v) !== -1;

    })) res.push(v);

    return res;

}, []);

DEMO: http://jsfiddle.net/nWjcp/4/