mirror of
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Merge branch 'MDL-6340' of git://github.com/timhunt/moodle
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David Monllao
223
question/classes/bank/random_question_loader.php
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223
question/classes/bank/random_question_loader.php
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<?php
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// This file is part of Moodle - http://moodle.org/
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//
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// Moodle is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// Moodle is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with Moodle. If not, see <http://www.gnu.org/licenses/>.
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/**
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* A class for efficiently finds questions at random from the question bank.
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*
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* @package core_question
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* @copyright 2015 The Open University
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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namespace core_question\bank;
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/**
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* This class efficiently finds questions at random from the question bank.
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*
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* You can ask for questions at random one at a time. Each time you ask, you
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* pass a category id, and whether to pick from that category and all subcategories
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* or just that category.
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*
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* The number of teams each question has been used is tracked, and we will always
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* return a question from among those elegible that has been used the fewest times.
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* So, if there are questions that have not been used yet in the category asked for,
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* one of those will be returned. However, within one instantiation of this class,
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* we will never return a given question more than once, and we will never return
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* questions passed into the constructor as $usedquestions.
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*
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* @copyright 2015 The Open University
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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class random_question_loader {
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/** @var \qubaid_condition which usages to consider previous attempts from. */
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protected $qubaids;
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/** @var array qtypes that cannot be used by random questions. */
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protected $excludedqtypes;
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/** @var array categoryid & include subcategories => num previous uses => questionid => 1. */
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protected $availablequestionscache = array();
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/**
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* @var array questionid => num recent uses. Questions that have been used,
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* but that is not yet recorded in the DB.
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*/
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protected $recentlyusedquestions;
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/**
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* Constructor.
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* @param \qubaid_condition $qubaids the usages to consider when counting previous uses of each question.
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* @param array $usedquestions questionid => number of times used count. If we should allow for
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* further existing uses of a question in addition to the ones in $qubaids.
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*/
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public function __construct(\qubaid_condition $qubaids, array $usedquestions = array()) {
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$this->qubaids = $qubaids;
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$this->recentlyusedquestions = $usedquestions;
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foreach (\question_bank::get_all_qtypes() as $qtype) {
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if (!$qtype->is_usable_by_random()) {
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$this->excludedqtypes[] = $qtype->name();
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}
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}
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}
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/**
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* Pick a question at random from the given category, from among those with the fewest uses.
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*
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* It is up the the caller to verify that the cateogry exists. An unknown category
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* behaves like an empty one.
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*
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* @param int $categoryid the id of a category in the question bank.
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* @param bool $includesubcategories wether to pick a question from exactly
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* that category, or that category and subcategories.
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* @return int|null the id of the question picked, or null if there aren't any.
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*/
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public function get_next_question_id($categoryid, $includesubcategories) {
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$this->ensure_questions_for_category_loaded($categoryid, $includesubcategories);
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$categorykey = $this->get_category_key($categoryid, $includesubcategories);
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if (empty($this->availablequestionscache[$categorykey])) {
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return null;
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}
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reset($this->availablequestionscache[$categorykey]);
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$lowestcount = key($this->availablequestionscache[$categorykey]);
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reset($this->availablequestionscache[$categorykey][$lowestcount]);
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$questionid = key($this->availablequestionscache[$categorykey][$lowestcount]);
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$this->use_question($questionid);
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return $questionid;
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}
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/**
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* Get the key into {@link $availablequestionscache} for this combination of options.
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* @param int $categoryid the id of a category in the question bank.
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* @param bool $includesubcategories wether to pick a question from exactly
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* that category, or that category and subcategories.
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* @return string the cache key.
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*/
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protected function get_category_key($categoryid, $includesubcategories) {
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if ($includesubcategories) {
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return $categoryid . '|1';
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} else {
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return $categoryid . '|0';
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}
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}
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/**
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* Populate {@link $availablequestionscache} for this combination of options.
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* @param int $categoryid the id of a category in the question bank.
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* @param bool $includesubcategories wether to pick a question from exactly
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* that category, or that category and subcategories.
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*/
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protected function ensure_questions_for_category_loaded($categoryid, $includesubcategories) {
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global $DB;
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$categorykey = $this->get_category_key($categoryid, $includesubcategories);
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if (isset($this->availablequestionscache[$categorykey])) {
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// Data is already in the cache, nothing to do.
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return;
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}
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// Load the available questions from the question bank.
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if ($includesubcategories) {
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$categoryids = question_categorylist($categoryid);
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} else {
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$categoryids = array($categoryid);
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}
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list($extraconditions, $extraparams) = $DB->get_in_or_equal($this->excludedqtypes,
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SQL_PARAMS_NAMED, 'excludedqtype', false);
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$questionidsandcounts = \question_bank::get_finder()->get_questions_from_categories_with_usage_counts(
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$categoryids, $this->qubaids, 'q.qtype ' . $extraconditions, $extraparams);
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if (!$questionidsandcounts) {
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// No questions in this category.
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$this->availablequestionscache[$categorykey] = array();
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return;
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}
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// Put all the questions with each value of $prevusecount in separate arrays.
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$idsbyusecount = array();
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foreach ($questionidsandcounts as $questionid => $prevusecount) {
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if (isset($this->recentlyusedquestions[$questionid])) {
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// Recently used questions are never returned.
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continue;
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}
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$idsbyusecount[$prevusecount][] = $questionid;
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}
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// Now put that data into our cache. For each count, we need to shuffle
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// questionids, and make those the keys of an array.
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$this->availablequestionscache[$categorykey] = array();
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foreach ($idsbyusecount as $prevusecount => $questionids) {
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shuffle($questionids);
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$this->availablequestionscache[$categorykey][$prevusecount] = array_combine(
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$questionids, array_fill(0, count($questionids), 1));
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}
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ksort($this->availablequestionscache[$categorykey]);
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}
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/**
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* Update the internal data structures to indicate that a given question has
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* been used one more time.
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*
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* @param int $questionid the question that is being used.
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*/
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protected function use_question($questionid) {
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if (isset($this->recentlyusedquestions[$questionid])) {
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$this->recentlyusedquestions[$questionid] += 1;
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} else {
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$this->recentlyusedquestions[$questionid] = 1;
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}
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foreach ($this->availablequestionscache as $categorykey => $questionsforcategory) {
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foreach ($questionsforcategory as $numuses => $questionids) {
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if (!isset($questionids[$questionid])) {
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continue;
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}
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unset($this->availablequestionscache[$categorykey][$numuses][$questionid]);
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if (empty($this->availablequestionscache[$categorykey][$numuses])) {
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unset($this->availablequestionscache[$categorykey][$numuses]);
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}
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}
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}
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}
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/**
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* Check whether a given question is available in a given category. If so, mark it used.
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*
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* @param int $categoryid the id of a category in the question bank.
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* @param bool $includesubcategories wether to pick a question from exactly
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* that category, or that category and subcategories.
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* @param int $questionid the question that is being used.
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* @return bool whether the question is available in the requested category.
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*/
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public function is_question_available($categoryid, $includesubcategories, $questionid) {
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$this->ensure_questions_for_category_loaded($categoryid, $includesubcategories);
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$categorykey = $this->get_category_key($categoryid, $includesubcategories);
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foreach ($this->availablequestionscache[$categorykey] as $questionids) {
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if (isset($questionids[$questionid])) {
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$this->use_question($questionid);
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return true;
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}
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}
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return false;
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}
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}
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128
question/classes/engine/variants/least_used_strategy.php
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128
question/classes/engine/variants/least_used_strategy.php
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@@ -0,0 +1,128 @@
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<?php
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// This file is part of Moodle - http://moodle.org/
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//
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// Moodle is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// Moodle is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with Moodle. If not, see <http://www.gnu.org/licenses/>.
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/**
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* A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
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*
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* @package core_question
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* @copyright 2015 The Open University
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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namespace core_question\engine\variants;
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defined('MOODLE_INTERNAL') || die();
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/**
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* A {@link \question_variant_selection_strategy} that randomly selects variants that were not used yet.
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*
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* If all variants have been used at least once in the set of usages under
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* consideration, then then it picks one of the least often used.
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*
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* Within one particular use of this class, each seed will always select the
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* same variant. This is so that shared datasets work in calculated questions,
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* and similar features in question types like varnumeric and STACK.
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*
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* @copyright 2015 The Open University
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* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
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*/
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class least_used_strategy implements \question_variant_selection_strategy {
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/** @var array seed => variant number => number of uses. */
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protected $variantsusecounts = array();
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/** @var array seed => variant number. */
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protected $selectedvariant = array();
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/**
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* Constructor.
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* @param question_usage_by_activity $quba the question usage we will be picking variants for.
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* @param qubaid_condition $qubaids ids of the usages to consider when counting previous uses of each variant.
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*/
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public function __construct(\question_usage_by_activity $quba, \qubaid_condition $qubaids) {
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$questionidtoseed = array();
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foreach ($quba->get_attempt_iterator() as $qa) {
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$question = $qa->get_question();
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if ($question->get_num_variants() > 1) {
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$questionidtoseed[$question->id] = $question->get_variants_selection_seed();
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}
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}
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if (empty($questionidtoseed)) {
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return;
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}
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$this->variantsusecounts = array_fill_keys($questionidtoseed, array());
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$variantsused = \question_engine::load_used_variants(array_keys($questionidtoseed), $qubaids);
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foreach ($variantsused as $questionid => $usagecounts) {
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$seed = $questionidtoseed[$questionid];
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foreach ($usagecounts as $variant => $count) {
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if (isset($this->variantsusecounts[$seed][$variant])) {
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$this->variantsusecounts[$seed][$variant] += $count;
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} else {
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$this->variantsusecounts[$seed][$variant] = $count;
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}
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}
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}
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}
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public function choose_variant($maxvariants, $seed) {
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if ($maxvariants == 1) {
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return 1;
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}
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if (isset($this->selectedvariant[$seed])) {
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return $this->selectedvariant[$seed];
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}
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if ($maxvariants > 2 * count($this->variantsusecounts[$seed])) {
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// Many many more variants exist than have been used so far.
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// It will be quicker to just pick until we miss a collision.
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do {
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$variant = rand(1, $maxvariants);
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} while (isset($this->variantsusecounts[$seed][$variant]));
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} else {
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// We need to work harder to find a least-used one.
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$leastusedvariants = array();
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for ($variant = 1; $variant <= $maxvariants; ++$variant) {
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if (!isset($this->variantsusecounts[$seed][$variant])) {
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$leastusedvariants[$variant] = 1;
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}
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}
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if (empty($leastusedvariants)) {
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// All variants used at least once, try again.
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$leastuses = min($this->variantsusecounts[$seed]);
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foreach ($this->variantsusecounts[$seed] as $variant => $uses) {
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if ($uses == $leastuses) {
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$leastusedvariants[$variant] = 1;
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}
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}
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}
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$variant = array_rand($leastusedvariants);
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}
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$this->selectedvariant[$seed] = $variant;
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if (isset($variantsusecounts[$seed][$variant])) {
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$variantsusecounts[$seed][$variant] += 1;
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} else {
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$variantsusecounts[$seed][$variant] = 1;
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}
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return $variant;
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}
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}
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Reference in New Issue
Block a user