teacherTimeEfficiency with max 2 lesson in dayOfWeek?

[hangocanh2303]

In school timetabling, function teacherTimeEfficiency. Sometimes timefold sets 3 or 4 consecutive lessons of the same teacher in 1 dayOfWeek.

Constraint teacherTimeEfficiency(ConstraintFactory constraintFactory) {
    // A teacher prefers to teach sequential lessons and dislikes gaps between lessons.
    return constraintFactory
            .forEach(Lesson.class)
            .join(Lesson.class, Joiners.equal(Lesson::getTeacher),
                    Joiners.equal((lesson) -> lesson.getTimeslot().getDayOfWeek()))
            .filter((lesson1, lesson2) -> {
                Duration between = Duration.between(lesson1.getTimeslot().getEndTime(),
                        lesson2.getTimeslot().getStartTime());
                return !between.isNegative() && between.compareTo(Duration.ofMinutes(30)) <= 0;
            })
            .reward(HardSoftScore.ONE_SOFT)
            .justifyWith((lesson1, lesson2, score) -> new TeacherTimeEfficiencyJustification(lesson1.getTeacher(), lesson1, lesson2))
            .asConstraint("Teacher time efficiency");
}

How to set priority 2 consecutive lessons with some subjects like literature or math?

[Christopher-Chianelli]

There are various ways:

1. joins + ifNotExists, which can only be used if you know the number of consecutive lessons in advance (in this case, 2)

private static boolean isConsecutive(Lesson a, Lesson b) {
    Duration between = Duration.between(lesson1.getTimeslot().getEndTime(),
                        lesson2.getTimeslot().getStartTime());
    return !between.isNegative() && between.compareTo(Duration.ofMinutes(30)) <= 0;
}

Constraint teacherTimeEfficiency(ConstraintFactory constraintFactory) {
    // A teacher prefers to teach sequential lessons and dislikes gaps between lessons.
    return constraintFactory
            .forEach(Lesson.class)
            .join(Lesson.class, Joiners.equal(Lesson::getTeacher),
                    Joiners.equal((lesson) -> lesson.getTimeslot().getDayOfWeek()))
            // can do a filter here to check for subject
            .filter(SchoolTimetablingConstraintProvider::isConsecutive)
            .ifNotExist(Lesson.class,
                                Joiners.equal(Lesson::getTeacher),
                                Joiners.equal((lesson) -> lesson.getTimeslot().getDayOfWeek()),
                                // lesson1 is before lesson2
                                // check if lesson3 is consecutively before lesson1 or consecutively after lesson2
                                Joiners.filtering((lesson1, lesson2, lesson3) -> isConsecutive(lesson3, lesson1) || isConsecutive(lesson2, lesson3))
            )
            .reward(HardSoftScore.ONE_SOFT)
            .justifyWith((lesson1, lesson2, score) -> new TeacherTimeEfficiencyJustification(lesson1.getTeacher(), lesson1, lesson2))
            .asConstraint("Teacher time efficiency 2 consecutive lessons");
}

2. groupBy + toConnectedRanges, which can work with a dynamic number of consecutive lessons:

Constraint teacherTimeEfficiency(ConstraintFactory constraintFactory) {
    // A teacher prefers to teach sequential lessons and dislikes gaps between lessons.
    return constraintFactory
            .forEach(Lesson.class)
            .groupBy(
                          // If you want consecutive lessons on the same subject, uncomment the next line
                          // lesson -> lesson.getSubject(),
                          lesson -> lesson.getTimeslot().getDayOfWeek(),
                          ConstraintCollectors.toConnectedTemporalRanges(
                              lesson -> lesson.getTimeslot().getStartTime(),
                              lesson -> lesson.getTimeslot().getEndTime())
            )
            .flattenLast(ConnectedRangeChain::getConnectedRanges)
            .filter((day, connectedRange) -> connectedRange.
getContainedRangeCount() == 2)  // note:  overlapping lessons would be counted as consecutive, but that usually handled by a hard constraint
            .reward(HardSoftScore.ONE_SOFT)
            .asConstraint("Teacher time efficiency 2 consecutive lessons");

}

[hangocanh2303]

@Christopher-Chianelli thanks
Can I ask you one more question? Currently, when configuring the solverconfig.xml, if I declare move selectors such as:

<changeMoveSelector>
    <!-- Apply the filter only for Timeslot planning value -->
    <filterClass>org.acme.schooltimetabling.filter.LessonFilter</filterClass>
    <valueSelector variableName="timeslot"/>
</changeMoveSelector>

then my algorithm's result worsens. If I don't want to declare a move selector in the XML and want to use the default move selector (without declaring anything), how can I declare the filterClass with the default move selector?

[Christopher-Chianelli]

As far as I am aware, there is no option to apply a filter without configuring selectors. As for what the default selector looks like:

<unionMoveSelector>
  <changeMoveSelector />
  <swapMoveSelector />
</unionMoveSelector>