20 lines
839 B
Markdown
20 lines
839 B
Markdown
### Standard deviation
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Use `Array.reduce()` to calculate the mean of the values, the variance of the values, and the sum of the variance
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of the values to determine the standard deviation of an array of numbers.
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Since there are two types of standard deviation, population and sample, you can use a flag to switch to population (sample is default).
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```js
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const standardDeviation = (arr, usePopulation) => {
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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 / arr.length, 2)), [])
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.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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// 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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