diff --git a/snippets/standard-deviation.md b/snippets/standard-deviation.md new file mode 100644 index 000000000..e559972bb --- /dev/null +++ b/snippets/standard-deviation.md @@ -0,0 +1,17 @@ +### Standard deviation + +Use `Array.reduce()` to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then +determine the standard deviation. +You can omit the second argument 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(Math.pow(val - mean, 2)), []) + .reduce((acc, val) => acc + val, 0) / (arr.length - (usePopulation ? 0 : 1)) + ); + } +// standardDeviation([10,2,38,23,38,23,21]) -> 13.284434142114991 (sample) +// standardDeviation([10,2,38,23,38,23,21], true) -> 12.29899614287479 (population) +```