stddev with typescript

standardDeviation.ts

const average = (arr: number[]): number => arr.reduce((p, c) => p + c, 0) / arr.length;

const standardDeviation = (values: number[]) => {
  const avg = average(values);

  const squareDiffs = values.map((value) => {
    let diff = value - avg;
    let sqrDiff = diff * diff;
    return sqrDiff;
  });

  const avgSquareDiff = average(squareDiffs);

  return Math.sqrt(avgSquareDiff);
};

const values = [{i: 2, x: '42'}, {i: 0, x: '21'}, {i: 3, x: '84'}, {i: 1, x: '168'}]

const stdDev = Number(standardDeviation(values.map((data) => Number(data.x)))).toFixed(3);

console.log(stdDev) // 56.300