31 lines
994 B
Markdown
31 lines
994 B
Markdown
---
|
|
title: Standard deviation
|
|
tags: math
|
|
cover: interior-16
|
|
firstSeen: 2017-12-17T17:55:51+02:00
|
|
lastUpdated: 2020-10-22T20:24:30+03:00
|
|
---
|
|
|
|
Calculates the standard deviation of an array of numbers.
|
|
|
|
- Use `Array.prototype.reduce()` to calculate the mean, variance and the sum of the variance of the values and determine the standard deviation.
|
|
- Omit the second argument, `usePopulation`, to get the sample standard deviation or set it to `true` to get the population standard deviation.
|
|
|
|
```js
|
|
const standardDeviation = (arr, usePopulation = false) => {
|
|
const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
|
|
return Math.sqrt(
|
|
arr
|
|
.reduce((acc, val) => acc.concat((val - mean) ** 2), [])
|
|
.reduce((acc, val) => acc + val, 0) /
|
|
(arr.length - (usePopulation ? 0 : 1))
|
|
);
|
|
};
|
|
```
|
|
|
|
```js
|
|
standardDeviation([10, 2, 38, 23, 38, 23, 21]); // 13.284434142114991 (sample)
|
|
standardDeviation([10, 2, 38, 23, 38, 23, 21], true);
|
|
// 12.29899614287479 (population)
|
|
```
|