Simple Rolling Average function

roller.js

/* Fergus In London - https://fergus.london - <fergus@fergus.london>
 *
 * Simple little function for calculating rolling averages, both simple and
 *  weighted. Example can be found on the GitHub Gist, or on my website.
 *
 * Do as you please, no rights reserved and no warranties provided. :)
 */


/**
 * Constructs a new "roller" function.
 *
 * @param Number   Defaults to 10
 * @param Boolean  Defaults to false
 * @return Function
 */
var roller = function(limit, weighted) {
  // Initialise Defaults
    limit     = limit || 10;
    weighted  = weighted || false;

  // Instance Variables
    var points = [];

  // Calculates an Average; either weighted (linear) or standard.
    function calculateAverage() {
        return (function(sum, data, n){
            /* Sum of Consecutive Integers */
            var weightbase = (n * (n+1)) / 2;

            for(var i = 0; i < n; i++)
              sum += (weighted) ? data[i] * ((i+1) / weightbase) : data[i];

            return sum;
        })(0, points, points.length) / ((weighted) ? 1 : points.length);
    };


    /**
     * Adds the value to the internal list, ensuring the list adheres to the
     *  confines defined by the user during construction, and then returns the
     *  average.
     *
     * @param Number
     * @return Number|NaN 
     */
    return function(val) {
        if (isNaN(val)) return NaN;

        points.push(val);
        if( points.length > limit ) points.shift();

        return calculateAverage();
    };
};

Example Usage

Simple Rolling Average

var rolling = roller(5),
    tests = [
  // IN   OUT 
  [  6  ,  6  ],
  [  3  , 4.5 ],
  [  1  , 3.3 ],
  [  10 ,  5  ],
  [  5  ,  5  ],
  [  7  , 5.2 ]
];

tests.forEach(function(test){
  var result = rolling(test[0]);
  console.log("Input: "+ test[0] +". Output: "+ result);

  if (result.toFixed(1) != test[1])
    throw "Incorrect Value Returned! (Expected "+ test[1] +")";
});

Weighted Rolling Average

var rolling = roller(5, true), result = 0;

[77, 79, 79, 81, 83].forEach(function(num){
   result = rolling(num);
});

console.log("Weighted Rolling Average: "+ result);
if (result.toFixed(2) != 80.73)
  throw "Incorrected Value Returned! (Expected 80.73)";