Simple stddev example

stddev.js

var curry = require('lodash.curry');

var counts = [9, 4, 4, 5, 49];
var avgCount = mean(counts);
var deviations = counts.map(curry(bMinusA)(avgCount));
var squaredDevs = deviations.map(square);
var variance = mean(squaredDevs);
var populationStdDev =  Math.sqrt(variance);
console.log('avgCount', avgCount);
console.log('populationStdDev', populationStdDev);

function sum(count, total) {
  return total + count;
}

function bMinusA(a, b) {
  return b - a;
}

function square(x) {
  return x * x;
}

function mean(values) {
  return values.reduce(sum, 0)/values.length;
}