queue_stats-8.x-1.0-beta1/src/Statistics/ExponentialMovingAverage.php

<?php

namespace Drupal\queue_stats\Statistics;

/**
 * Exponential moving average.
 *
 * This allows us to store only previous averages and number of items instead
 * of individual values.
 */
class ExponentialMovingAverage {

  /**
   * The number of items which the statistics are based on.
   *
   * @var int
   */
  protected $numItems = 0;


  /**
   * The average.
   *
   * @var float
   */
  protected $average = 0;

  /**
   * The exponential weighted moving average factor.
   *
   * This is a constant that affects how quickly the average "catches up" to the
   * latest trend. Smaller the number the faster. (At 1 it's no longer an
   * average and just becomes the latest value.)
   *
   * @var int
   */
  protected $factor;

  /**
   * ExponentialMovingAverage constructor.
   *
   * @param int $factor
   *   The exponential weighted moving average factor.
   */
  public function __construct(int $factor) {
    $this->factor = $factor;
  }

  /**
   * Adds a value to the exponential moving average.
   */
  public function add($value) {
    $this->numItems++;
    $this->average = $this->average + (($value - $this->average) / min($this->factor, $this->numItems));
    return $this->average;
  }

  /**
   * Returns the exponential moving average.
   *
   * @return float
   *   The exponential moving average.
   */
  public function average() {
    return $this->average;
  }

}