Math/Statistics.js

  1. /** A helper class containing statistics methods. */
  2. Lore.Statistics = class Statistics {
  3.     /**
  4.      * Returns a normally distributed (pseudo) random number.
  5.      * 
  6.      * @returns {Number} A normally distributed (pseudo) random number.
  7.      */
  8.     static randomNormal() {
  9.         let val, u, v, s, mul;
  11.         if (Lore.Statistics.spareRandomNormal !== null) {
  12.             val = Lore.Statistics.spareRandomNormal;
  13.             Lore.Statistics.spareRandomNormal = null;
  14.         } else {
  15.             do {
  16.                 u = Math.random() * 2 - 1;
  17.                 v = Math.random() * 2 - 1;
  19.                 s = u * u + v * v;
  20.             } while (s === 0 || s >= 1);
  22.             mul = Math.sqrt(-2 * Math.log(s) / s);
  23.             val = u * mul;
  24.             Lore.Statistics.spareRandomNormal = v * mul;
  25.         }
  27.         return val / 14;
  28.     }
  30.     /**
  31.      * Returns a normally distributed (pseudo) random number within a range.
  32.      * 
  33.      * @param {Number} a The start of the range.
  34.      * @param {Number} b The end of the range.
  35.      * @returns {Number} A normally distributed (pseudo) random number within a range.
  36.      */
  37.     static randomNormalInRange(a, b) {
  38.         let val;
  40.         do {
  41.             val = Lore.Statistics.randomNormal();
  42.         } while (val < a || val > b);
  44.         return val;
  45.     }
  47.     /**
  48.      * Returns a normally distributed (pseudo) random number around a mean with a standard deviation.
  49.      * 
  50.      * @param {Number} mean The mean.
  51.      * @param {Number} sd The standard deviation.
  52.      * @returns {Number} A normally distributed (pseudo) random number around a mean with a standard deviation.
  53.      */
  54.     static randomNormalScaled(mean, sd) {
  55.         let r = Lore.Statistics.randomNormalInRange(-1, 1);
  56.         
  57.         return r * sd + mean;
  58.     }
  60.     /**
  61.      * Normalize / scale an array between 0 and 1.
  62.      * 
  63.      * @param {Number[]} arr An array.
  64.      * @returns {Number[]} The normalized / scaled array.
  65.      */
  66.     static normalize(arr) {
  67.         let newArr = arr.slice();
  68.         let max = Number.NEGATIVE_INFINITY;
  69.         let min = Number.POSITIVE_INFINITY;
  71.         for (let i = 0; i < newArr.length; i++) {
  72.             let val = newArr[i];
  73.             if (val > max) max = val;
  74.             if (val < min) min = val;
  75.         }
  77.         let diff = max - min;
  79.         for (let i = 0; i < newArr.length; i++) {
  80.             newArr[i] = (newArr[i] - min) / diff;
  81.         }
  82.         
  83.         return newArr;
  84.     }
  86.     /**
  87.      * Scales a number to within a given scale.
  88.      * 
  89.      * @param {Number} value The number.
  90.      * @param {Number} oldMin The current minimum.
  91.      * @param {Number} oldMax The current maximum.
  92.      * @param {Number} newMin The cnew minimum.
  93.      * @param {Number} newMax The new maximum.
  94.      * @returns {Number} The scaled number.
  95.      */
  96.     static scale(value, oldMin, oldMax, newMin, newMax) {
  97.         return (newMax - newMin) * (value - oldMin) / (oldMax - oldMin) + newMin;
  98.     }
  99. }
  101. Lore.Statistics.spareRandomNormal = null;