Standard Deviation snippets (terse & verbose)

math-std-dev.js

// explained
function calculateStandardDeviation(numbers) {
  // Calculate the mean of the array of numbers
  const mean = numbers.reduce((a, b) => a + b, 0) / numbers.length;

  // Calculate the differences between the numbers and the mean
  const differences = numbers.map(num => num - mean);

  // Square each of the differences
  const squaredDifferences = differences.map(diff => diff ** 2);

  // Add all of the squared differences together
  const sumSquaredDifferences = squaredDifferences.reduce((a, b) => a + b, 0);

  // Divide the sum of the squared differences by the total number of numbers in the array
  const variance = sumSquaredDifferences / numbers.length;

  // Take the square root of the variance to get the standard deviation
  const standardDeviation = Math.sqrt(variance);

  return standardDeviation;
}
const numbers = [0, 1, 1, 3, 2, 1, 0, 3, 6, 2, 2, 0];
const standardDeviation = calculateStandardDeviation(numbers);
console.log(standardDeviation); // Output: 1.63

//shortened
const std_dev = (numbers) => {
  const avg = n=>n.reduce((a=0,b)=>a+b)/n.length, mean = avg(numbers);
  return Math.sqrt(avg(numbers.map(n=>(n-mean)**2)));
}
console.log(std_dev([0, 1, 1, 3, 2, 1, 0, 3, 6, 2, 2, 0])); // Output: 1.63