Basic functions for stats

stats.js

function sum (arr) {
  return arr.reduce((x, i) => x + i, 0);
}

function mean (arr) {
  return sum(arr) / arr.length;
}

function variance (arr) {
  let m = mean(arr);
  let total = arr.reduce((x, i) => Math.pow( i - m, 2 ), 0);
  return total / arr.length;
}

function stdDev (arr) {
  return Math.sqrt( variance(arr) );
}