25 lines
915 B
Markdown
25 lines
915 B
Markdown
---
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title: standardDeviation
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tags: math,array,intermediate
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---
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Returns the standard deviation of an array of numbers.
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Use `Array.prototype.reduce()` to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then
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determine the standard deviation.
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You can omit the second argument to get the sample standard deviation or set it to `true` to get the population standard deviation.
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```js
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const standardDeviation = (arr, usePopulation = false) => {
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const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
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return Math.sqrt(
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arr.reduce((acc, val) => acc.concat((val - mean) ** 2), []).reduce((acc, val) => acc + val, 0) /
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(arr.length - (usePopulation ? 0 : 1))
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);
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};
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```
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```js
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standardDeviation([10, 2, 38, 23, 38, 23, 21]); // 13.284434142114991 (sample)
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standardDeviation([10, 2, 38, 23, 38, 23, 21], true); // 12.29899614287479 (population)
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``` |