18 lines
799 B
Markdown
18 lines
799 B
Markdown
### Standard deviation
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Use `Array.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(Math.pow(val - mean, 2)), [])
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.reduce((acc, val) => acc + val, 0) / (arr.length - (usePopulation ? 0 : 1))
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);
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}
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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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```
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