How to Implement a Custom Move to Swap Multiple Periods (Grouped by Timespan)?

[ace19wre]

Hi everyone,

First off, big thanks to the Timefold community! My college scheduling model is nearly complete, and I’ve been able to reach this point thanks to the resources and helpful folks here.

My generated timetable correctly satisfies all hard constraints (like no student overlap and time rules). Here's a snapshot of the result:
Schedule

Right now, I’m noticing that:

• 2-hour practicals are getting grouped on a few specific days.
• 1-hour lectures are similarly being grouped together.

This makes the weekly schedule unbalanced, even though it’s technically feasible.

I attempted to use load-balancing constraints to spread different session types across the week, but, The inbuilt swap moves result in highly negative scores because they operate on individual lessons, which causes impractical intermediate states. As a result, the solver quickly undoes them.

I believe the right solution is to implement a custom move that can:

• Swap multiple periods together — for example, all lessons in a 2-hour block.
• Respect their timeslot grouping when making the move.
• Improve or preserve score better than naive single-entity swaps.

My question:
How can I define a move that acts on a group of planning entities (e.g., all periods within a timespan)?

Are there any code examples or best practices for implementing grouped or timespan-aware moves?

[ge0ffrey]

With a custom move you can implement this, see MoveIteratorFactory in the docs.

That being said, note that we're working on a much easier and powerful way to implements custom moves, codename "move streams", but that will take a good while still.

[ace19wre]

Maybe a dumb question but where should I put my custom moves in the project structure, is there a convention reference?

[Christopher-Chianelli]

Wherever your want/wherever is most convenient for you. Timefold Solver doesn't care where your classes are. If you need a suggestion, you could put it inside a solver subpackage.