Javascript - Calculating Standard Deviations

JavascriptCalculatingStandardDeviations.md

Javascript - Calculating Standard Deviations

This is based on a excellent post by Derick Bailey.

function standardDeviation(values){
  var avg = average(values);
  
  var squareDiffs = values.map(function(value){
    var diff = value - avg;
    var sqrDiff = diff * diff;
    return sqrDiff;
  });
  
  var avgSquareDiff = average(squareDiffs);
 
  var stdDev = Math.sqrt(avgSquareDiff);
  return stdDev;
}
 
function average(data){
  var sum = data.reduce(function(sum, value){
    return sum + value;
  }, 0);
 
  var avg = sum / data.length;
  return avg;
}

This can then be use like this:

> standardDeviation([1.34,1.78,1.67,0.98,0.56,1.65])

0.4351245032554858