mirror of
https://github.com/moodle/moodle.git
synced 2025-03-10 02:40:10 +01:00
bb93fc24aa
There are several improvements over what we had before: 1. We track all the questions seen in the the student's previous quiz attempts, so that when they start a new quiz attempt, they get questions they have not seen before if possible. 2. When there are no more unseen questions, we start repeating, but always taking from the questions with the fewest attempts so far. 3. A similar logic is applied with variants within one question. There is lots of credit to go around here. Oleg Sychev's students Alex Shkarupa, Sergei Bastrykin and Darya Beda all worked on this over several years, helping to clarify the problem and shape the best solution. In the end, their various attempts were rewritten into this final patch by me.
129 lines
4.9 KiB
PHP
129 lines
4.9 KiB
PHP
<?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.
|
|
*/
|
|
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];
|
|
}
|
|
|
|
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;
|
|
}
|
|
}
|