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See Release Notes

  • Bug fixes for general core bugs in 4.2.x will end 22 April 2024 (12 months).
  • Bug fixes for security issues in 4.2.x will end 7 October 2024 (18 months).
  • PHP version: minimum PHP 8.0.0 Note: minimum PHP version has increased since Moodle 4.1. PHP 8.1.x is supported too.
<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
 *
 * @package   core_question
 * @copyright 2015 The Open University
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */


namespace core_question\engine\variants;
defined('MOODLE_INTERNAL') || die();


/**
 * A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
 *
 * If all variants have been used at least once in the set of usages under
 * consideration, then then it picks one of the least often used.
 *
 * Within one particular use of this class, each seed will always select the
 * same variant. This is so that shared datasets work in calculated questions,
 * and similar features in question types like varnumeric and STACK.
 *
 * @copyright 2015 The Open University
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class least_used_strategy implements \question_variant_selection_strategy {

    /** @var array seed => variant number => number of uses. */
    protected $variantsusecounts = array();

    /** @var array seed => variant number. */
    protected $selectedvariant = array();

    /**
     * Constructor.
< * @param question_usage_by_activity $quba the question usage we will be picking variants for. < * @param qubaid_condition $qubaids ids of the usages to consider when counting previous uses of each variant.
> * @param \question_usage_by_activity $quba the question usage we will be picking variants for. > * @param \qubaid_condition $qubaids ids of the usages to consider when counting previous uses of each variant.
*/ public function __construct(\question_usage_by_activity $quba, \qubaid_condition $qubaids) { $questionidtoseed = array(); foreach ($quba->get_attempt_iterator() as $qa) { $question = $qa->get_question(); if ($question->get_num_variants() > 1) { $questionidtoseed[$question->id] = $question->get_variants_selection_seed(); } } if (empty($questionidtoseed)) { return; } $this->variantsusecounts = array_fill_keys($questionidtoseed, array()); $variantsused = \question_engine::load_used_variants(array_keys($questionidtoseed), $qubaids); foreach ($variantsused as $questionid => $usagecounts) { $seed = $questionidtoseed[$questionid]; foreach ($usagecounts as $variant => $count) { if (isset($this->variantsusecounts[$seed][$variant])) { $this->variantsusecounts[$seed][$variant] += $count; } else { $this->variantsusecounts[$seed][$variant] = $count; } } } } public function choose_variant($maxvariants, $seed) { if ($maxvariants == 1) { return 1; } if (isset($this->selectedvariant[$seed])) { return $this->selectedvariant[$seed]; } // Catch a possible programming error, and make the problem clear. if (!isset($this->variantsusecounts[$seed])) { debugging('Variant requested for unknown seed ' . $seed . '. ' . 'You must add all questions to the usage before creating the least_used_strategy. ' . 'Continuing, but the variant choses may not actually be least used.', DEBUG_DEVELOPER); $this->variantsusecounts[$seed] = array(); } if ($maxvariants > 2 * count($this->variantsusecounts[$seed])) { // Many many more variants exist than have been used so far. // It will be quicker to just pick until we miss a collision. do { $variant = rand(1, $maxvariants); } while (isset($this->variantsusecounts[$seed][$variant])); } else { // We need to work harder to find a least-used one. $leastusedvariants = array(); for ($variant = 1; $variant <= $maxvariants; ++$variant) { if (!isset($this->variantsusecounts[$seed][$variant])) { $leastusedvariants[$variant] = 1; } } if (empty($leastusedvariants)) { // All variants used at least once, try again. $leastuses = min($this->variantsusecounts[$seed]); foreach ($this->variantsusecounts[$seed] as $variant => $uses) { if ($uses == $leastuses) { $leastusedvariants[$variant] = 1; } } } $variant = array_rand($leastusedvariants); } $this->selectedvariant[$seed] = $variant; if (isset($variantsusecounts[$seed][$variant])) { $variantsusecounts[$seed][$variant] += 1; } else { $variantsusecounts[$seed][$variant] = 1; } return $variant; } }