Standard deviation javascript

Question

I am trying to get the standard deviation of a user input string. I have as follows, but it returns the wrong value for SD. The calculation should go as follows: Sum values/

Answer 1

Shorthand method for getting standard deviation from an array if you don't like lots of code:

function getStandardDeviation (array) {
  const n = array.length
  const mean = array.reduce((a, b) => a + b) / n
  return Math.sqrt(array.map(x => Math.pow(x - mean, 2)).reduce((a, b) => a + b) / n)
}