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javascript/snippets/filter-unique.md

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+---
+title: Filter unique array values
+type: snippet
+tags: [array]
+cover: tulips-and-reeds
+dateModified: 2020-11-02T19:41:00+02:00
+---
+
+Creates an array with the unique values filtered out.
+
+- Use the `Set` constructor and the spread operator (`...`) to create an array of the unique values in `arr`.
+- Use `Array.prototype.filter()` to create an array containing only the non-unique values.
+
+```js
+const filterUnique = arr =>
+  [...new Set(arr)].filter(i => arr.indexOf(i) !== arr.lastIndexOf(i));
+```
+
+```js
+filterUnique([1, 2, 2, 3, 4, 4, 5]); // [2, 4]
+```