Differences Between: [Versions 310 and 403] [Versions 311 and 403] [Versions 39 and 403] [Versions 400 and 403] [Versions 401 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 }
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