[Summary view]

Differences Between: [Versions 310 and 402] [Versions 310 and 403]

   1  <?php
   2  // This file is part of Moodle - http://moodle.org/
   3  //
   4  // Moodle is free software: you can redistribute it and/or modify
   5  // it under the terms of the GNU General Public License as published by
   6  // the Free Software Foundation, either version 3 of the License, or
   7  // (at your option) any later version.
   8  //
   9  // Moodle is distributed in the hope that it will be useful,
  10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  // GNU General Public License for more details.
  13  //
  14  // You should have received a copy of the GNU General Public License
  15  // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16  
  17  /**
  18   * A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
  19   *
  20   * @package   core_question
  21   * @copyright 2015 The Open University
  22   * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  23   */
  24  
  25  
  26  namespace core_question\engine\variants;
  27  defined('MOODLE_INTERNAL') || die();
  28  
  29  
  30  /**
  31   * A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
  32   *
  33   * If all variants have been used at least once in the set of usages under
  34   * consideration, then then it picks one of the least often used.
  35   *
  36   * Within one particular use of this class, each seed will always select the
  37   * same variant. This is so that shared datasets work in calculated questions,
  38   * and similar features in question types like varnumeric and STACK.
  39   *
  40   * @copyright 2015 The Open University
  41   * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  42   */
  43  class least_used_strategy implements \question_variant_selection_strategy {
  44  
  45      /** @var array seed => variant number => number of uses. */
  46      protected $variantsusecounts = array();
  47  
  48      /** @var array seed => variant number. */
  49      protected $selectedvariant = array();
  50  
  51      /**
  52       * Constructor.
  53       * @param question_usage_by_activity $quba the question usage we will be picking variants for.
  54       * @param qubaid_condition $qubaids ids of the usages to consider when counting previous uses of each variant.
  55       */
  56      public function __construct(\question_usage_by_activity $quba, \qubaid_condition $qubaids) {
  57          $questionidtoseed = array();
  58          foreach ($quba->get_attempt_iterator() as $qa) {
  59              $question = $qa->get_question();
  60              if ($question->get_num_variants() > 1) {
  61                  $questionidtoseed[$question->id] = $question->get_variants_selection_seed();
  62              }
  63          }
  64  
  65          if (empty($questionidtoseed)) {
  66              return;
  67          }
  68  
  69          $this->variantsusecounts = array_fill_keys($questionidtoseed, array());
  70  
  71          $variantsused = \question_engine::load_used_variants(array_keys($questionidtoseed), $qubaids);
  72          foreach ($variantsused as $questionid => $usagecounts) {
  73              $seed = $questionidtoseed[$questionid];
  74              foreach ($usagecounts as $variant => $count) {
  75                  if (isset($this->variantsusecounts[$seed][$variant])) {
  76                      $this->variantsusecounts[$seed][$variant] += $count;
  77                  } else {
  78                      $this->variantsusecounts[$seed][$variant] = $count;
  79                  }
  80              }
  81          }
  82      }
  83  
  84      public function choose_variant($maxvariants, $seed) {
  85          if ($maxvariants == 1) {
  86              return 1;
  87          }
  88  
  89          if (isset($this->selectedvariant[$seed])) {
  90              return $this->selectedvariant[$seed];
  91          }
  92  
  93          // Catch a possible programming error, and make the problem clear.
  94          if (!isset($this->variantsusecounts[$seed])) {
  95              debugging('Variant requested for unknown seed ' . $seed . '. ' .
  96                      'You must add all questions to the usage before creating the least_used_strategy. ' .
  97                      'Continuing, but the variant choses may not actually be least used.',
  98                      DEBUG_DEVELOPER);
  99              $this->variantsusecounts[$seed] = array();
 100          }
 101  
 102          if ($maxvariants > 2 * count($this->variantsusecounts[$seed])) {
 103              // Many many more variants exist than have been used so far.
 104              // It will be quicker to just pick until we miss a collision.
 105              do {
 106                  $variant = rand(1, $maxvariants);
 107              } while (isset($this->variantsusecounts[$seed][$variant]));
 108  
 109          } else {
 110              // We need to work harder to find a least-used one.
 111              $leastusedvariants = array();
 112              for ($variant = 1; $variant <= $maxvariants; ++$variant) {
 113                  if (!isset($this->variantsusecounts[$seed][$variant])) {
 114                      $leastusedvariants[$variant] = 1;
 115                  }
 116              }
 117              if (empty($leastusedvariants)) {
 118                  // All variants used at least once, try again.
 119                  $leastuses = min($this->variantsusecounts[$seed]);
 120                  foreach ($this->variantsusecounts[$seed] as $variant => $uses) {
 121                      if ($uses == $leastuses) {
 122                          $leastusedvariants[$variant] = 1;
 123                      }
 124                  }
 125              }
 126              $variant = array_rand($leastusedvariants);
 127          }
 128  
 129          $this->selectedvariant[$seed] = $variant;
 130          if (isset($variantsusecounts[$seed][$variant])) {
 131              $variantsusecounts[$seed][$variant] += 1;
 132          } else {
 133              $variantsusecounts[$seed][$variant] = 1;
 134          }
 135          return $variant;
 136      }
 137  }