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Add usePopulation flag param

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atomiks
2017-12-13 23:41:28 +11:00
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parent 731df31395
commit b844b0f765
1 changed files with 5 additions and 5 deletions
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snippets/standard-deviation.md
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@ -3,15 +3,15 @@
Use `Array.reduce()` to calculate the mean of the values, the variance of the values, and the sum of the variance Use `Array.reduce()` to calculate the mean of the values, the variance of the values, and the sum of the variance
of the values to determine the standard deviation of an array of numbers. of the values to determine the standard deviation of an array of numbers.
NOTE: This is **population standard deviation**. Use `/ (arr.length - 1)` at the end to Since there are two types of standard deviation, population and sample, you can use a flag to switch to population (sample is default).
calculate **sample standard deviation**.
```js ```js
const standardDeviation = arr => const standardDeviation = (arr, usePopulation) =>
Math.sqrt( Math.sqrt(
arr.reduce((acc, val) => acc.concat(Math.pow(val - arr.reduce((acc, val) => acc + val, 0) / arr.length, 2)), []) arr.reduce((acc, val) => acc.concat(Math.pow(val - arr.reduce((acc, val) => acc + val, 0) / arr.length, 2)), [])
.reduce((acc, val) => acc + val, 0) .reduce((acc, val) => acc + val, 0)
/ arr.length / (arr.length - (usePopulation ? 0 : 1))
); );
// standardDeviation([10,2,38,23,38,23,21]) -> 12.298996142875 // standardDeviation([10,2,38,23,38,23,21]) -> 13.284434142114991 (sample)
// standardDeviation([10,2,38,23,38,23,21], true) -> 12.29899614287479 (population)
``` ```