find duplicates in two arrays

Question

I have two arrays like this:

var x = ['1','2','6'];
var y = ['4', '5','6'];

How do I find duplicates in two arrays in pure JavaScript and I would like to avoid using a loop?

Output - duplicates: 6

Does it need to be pure JS or can you use Underscore.js or jQuery? — ZeroBased_IX, Jul 10 '15 at 15:03
http://stackoverflow.com/questions/1885557/simplest-code-for-array-intersection-in-javascript — phts, Jul 10 '15 at 15:04
Similar quesiton [here](http://stackoverflow.com/questions/1885557/simplest-code-for-array-intersection-in-javascript) — leo.fcx, Jul 10 '15 at 15:04

score 2 · Accepted Answer · answered Jul 10 '15 at 15:08

2

Try something like this:

var x = ['1','2','6'];
var y = ['4', '5','6'];

var overlap = x.filter(function(v,i,a){
  return y.indexOf(v) > -1;
});

console.log(overlap); // ['6']

Does this work for your purpose?

MDN docs for filter

answered Jul 10 '15 at 15:08

1252748

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score 1 · Answer 2 · answered Jul 10 '15 at 15:09

1

Try this

var x = ['1','2','6'];
var y = ['4', '5','6'];
var duplicate = [];
for (var i=0; i<y.length; i++) {
    var index = x.indexOf(y[i]);
    if (index > -1) {
        duplicate.push(x[index]);
    }
}

Output: ["6"]

answered Jul 10 '15 at 15:09

SK.

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"I would like to avoid using a loop" – David Barker Jul 10 '15 at 15:10
@DavidBarker okay. It's `O(array1.length * array2.length)` but for reasonably small arrays and on modern hardware this shouldn't remotely cause an issue – SK. Jul 10 '15 at 15:14

find duplicates in two arrays

2 Answers2