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30-seconds-of-code/snippets/symmetricDifferenceWith.md
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2021-06-13 13:55:00 +03:00

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---
title: symmetricDifferenceWith
tags: array,intermediate
firstSeen: 2018-01-24T11:59:02+02:00
lastUpdated: 2020-10-18T14:58:09+03:00
---
Returns the symmetric difference between two arrays, using a provided function as a comparator.
- Use `Array.prototype.filter()` and `Array.prototype.findIndex()` to find the appropriate values.
```js
const symmetricDifferenceWith = (arr, val, comp) => [
...arr.filter(a => val.findIndex(b => comp(a, b)) === -1),
...val.filter(a => arr.findIndex(b => comp(a, b)) === -1)
];
```
```js
symmetricDifferenceWith(
[1, 1.2, 1.5, 3, 0],
[1.9, 3, 0, 3.9],
(a, b) => Math.round(a) === Math.round(b)
); // [1, 1.2, 3.9]
```