MDL-59786 analytics: Discard invalid samples

admin/tool/analytics/cli/guess_course_start_and_end.php

@@ -32,6 +32,8 @@ require_once($CFG->dirroot . '/course/format/weeks/lib.php');
 
 $help = "Guesses course start and end dates based on activity logs.
 
+IMPORTANT: Don't use this script if you keep previous academic years users enrolled in courses. Guesses would not be accurate.
+
 Options:
 --guessstart           Guess the course start date (default to true)
 --guessend             Guess the course end date (default to true)
@@ -183,10 +185,14 @@ function tool_analytics_calculate_course_dates($course, $options) {
 
                 $course->enddate = $guessedenddate;
 
-                if ($course->enddate > $course->startdate) {
-                    $notification .= PHP_EOL . '  ' . get_string('enddate') . ': ' . userdate($course->enddate);
-                } else {
+                $updateit = false;
+                if ($course->enddate < $course->startdate) {
                     $notification .= PHP_EOL . '  ' . get_string('errorendbeforestart', 'analytics', userdate($course->enddate));
+                } else if ($course->startdate + (YEARSECS + (WEEKSECS * 4)) > $course->enddate) {
+                    $notification .= PHP_EOL . '  ' . get_string('coursetoolong', 'analytics');
+                } else {
+                    $notification .= PHP_EOL . '  ' . get_string('enddate') . ': ' . userdate($course->enddate);
+                    $updateit = true;
                 }
 
                 if ($options['update']) {

lang/en/analytics.php

@@ -33,7 +33,7 @@ $string['enabledtimesplittings'] = 'Time splitting methods';
 $string['erroralreadypredict'] = '{$a} file has already been used to predict';
 $string['errorcannotreaddataset'] = 'Dataset file {$a} can not be read';
 $string['errorcannotwritedataset'] = 'Dataset file {$a} can not be written';
-$string['errorendbeforestart'] = 'The guessed end date ({$a}) is before the course start date.';
+$string['errorendbeforestart'] = 'The end date ({$a}) is before the course start date.';
 $string['errorinvalidindicator'] = 'Invalid {$a} indicator';
 $string['errorinvalidtimesplitting'] = 'Invalid time splitting, please ensure you added the class fully qualified class name';
 $string['errornoindicators'] = 'This model does not have any indicator';

lib/classes/analytics/target/course_dropout.php

@@ -115,7 +115,7 @@ class course_dropout extends \core_analytics\local\target\binary {
     }
 
     /**
-     * is_valid_analysable
+     * Discards courses that are not yet ready to be used for training or prediction.
      *
      * @param \core_analytics\analysable $course
      * @param bool $fortraining
@@ -147,13 +147,22 @@ class course_dropout extends \core_analytics\local\target\binary {
             return get_string('nocourseendtime');
         }
 
+        if ($course->get_end() < $course->get_start()) {
+            return get_string('errorendbeforestart', 'analytics');
+        }
+
+        // A course that lasts longer than 1 year probably have wrong start or end dates.
+        if ($course->get_end() - $course->get_start() > (YEARSECS + (WEEKSECS * 4))) {
+            return get_string('coursetoolong', 'analytics');
+        }
+
         // Ongoing courses data can not be used to train.
         if ($fortraining && !$course->is_finished()) {
             return get_string('coursenotyetfinished');
         }
 
         if ($fortraining) {
-            // Not a valid target for training if there are not enough course accesses.
+            // Not a valid target for training if there are not enough course accesses between the course start and end dates.
 
             $params = array('courseid' => $course->get_id(), 'anonymous' => 0, 'start' => $course->get_start(),
                 'end' => $course->get_end());
@@ -178,14 +187,39 @@ class course_dropout extends \core_analytics\local\target\binary {
     }
 
     /**
-     * All student enrolments are valid.
+     * Discard student enrolments that are invalid.
      *
      * @param int $sampleid
      * @param \core_analytics\analysable $course
      * @param bool $fortraining
-     * @return true|string
+     * @return bool
      */
     public function is_valid_sample($sampleid, \core_analytics\analysable $course, $fortraining = true) {
+
+        $userenrol = $this->retrieve('user_enrolments', $sampleid);
+        if ($userenrol->timeend && $course->get_start() > $userenrol->timeend) {
+            // Discard enrolments which time end is prior to the course start. This should get rid of
+            // old user enrolments that remain on the course.
+            return false;
+        }
+
+        $limit = $course->get_start() - (YEARSECS + (WEEKSECS * 4));
+        if (($userenrol->timestart && $userenrol->timestart < $limit) ||
+                (!$userenrol->timestart && $userenrol->timecreated < $limit)) {
+            // Following what we do in is_valid_sample, we will discard enrolments that last more than 1 academic year
+            // because they have incorrect start and end dates or because they are reused along multiple years
+            // without removing previous academic years students. This may not be very accurate because some courses
+            // can last just some months, but it is better than nothing and they will be flagged as drop out anyway
+            // in most of the cases.
+            return false;
+        }
+
+        if (($userenrol->timestart && $userenrol->timestart > $course->get_end()) ||
+                (!$userenrol->timestart && $userenrol->timecreated > $course->get_end())) {
+            // Discard user enrolments that starts after the analysable official end.
+            return false;
+        }
+
         return true;
     }
 

lib/classes/analytics/target/no_teaching.php

@@ -134,7 +134,7 @@ class no_teaching extends \core_analytics\local\target\binary {
      * @param int $sampleid
      * @param \core_analytics\analysable $analysable
      * @param bool $fortraining
-     * @return true|string
+     * @return bool
      */
     public function is_valid_sample($sampleid, \core_analytics\analysable $analysable, $fortraining = true) {