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javascript/snippets/sample-size.md

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+---
+title: N random elements in array
+type: snippet
+tags: [array,random]
+cover: tree-roots
+dateModified: 2020-10-22T20:24:30+03:00
+---
+
+Gets `n` random elements at unique keys from an array up to the size of the array.
+
+- Shuffle the array using the [Fisher-Yates algorithm](https://github.com/30-seconds/30-seconds-of-code#shuffle).
+- Use `Array.prototype.slice()` to get the first `n` elements.
+- Omit the second argument, `n`, to get only one element at random from the array.
+
+```js
+const sampleSize = ([...arr], n = 1) => {
+  let m = arr.length;
+  while (m) {
+    const i = Math.floor(Math.random() * m--);
+    [arr[m], arr[i]] = [arr[i], arr[m]];
+  }
+  return arr.slice(0, n);
+};
+```
+
+```js
+sampleSize([1, 2, 3], 2); // [3, 1]
+sampleSize([1, 2, 3], 4); // [2, 3, 1]
+```