Standard deviation

JavaScript, Math · Oct 22, 2020

Calculates the standard deviation of an array of numbers.

• Use `Array.prototype.reduce()` to calculate the mean, variance and the sum of the variance of the values and determine the standard deviation.
• Omit the second argument, `usePopulation`, to get the sample standard deviation or set it to `true` to get the population standard deviation.
```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((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)```

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