Biased random generator

BiasedRandom.js

function boundrand (min, max) {
  return min + (Math.random() * (max - min));
}

export default class BiasedRandom {

  /**
   * Ctor
   *
   * @example
   * // p means probability of this variant, r is for range of values generated
   * const probabilities = [ {p: 0.8, r: [1,5]}, {p: 0.2, r: [20,25]} ];
   * // v => v|0 is a filter for each generated value, example one is equal to Math.floor(v)
   * const weightGenerator = new BiasedRandom(probabilities, v => v|0);
   *
   * const weight = weightGenerator.generate();
   * // With a 80% probability weight will be between 1 and 5
   * // With a 20% probability weight will be between 20 and 25
   *
   * @param {Object[]} probabilities
   * @param filter
   */
  constructor (probabilities, filter = false) {
    this.probs = probabilities.sort((c, n) =>  c.p > n.p);
    this.filter = filter;

    if (!this._checkProbs()) {
      throw new Error('Sum of probabilities cannot be more than 1');
    }

    this.bounds = [];

    let bottomBound = 0;

    for (let i = 0; i < this.probs.length; i++) {
      const entry = this.probs[i];

      this.bounds.push([bottomBound, bottomBound + entry.p]);
      bottomBound = entry.p;
    }
  }

  _checkProbs () {
    return this.probs.reduce((acc,n)=>acc+=n.p,0) === 1;
  }

  /**
   * Generates value
   *
   * @returns {*}
   */
  generate () {
    const r = Math.random();

    for (let i = 0; i < this.probs.length; i++) {
      if (r > this.bounds[i][0] && r <= this.bounds[i][1]) {
        const v = boundrand(...this.probs[i].r);

        return (this.filter
          ? this.filter(v)
          : v);
      }
    }
  }
}