Thanks! I didn't create a separate category for learning-to-rank problems because they often overlap with other domains.

For example, some of the conservation competitions (https://mlcontests.com/state-of-competitive-machine-learning-2022/#conservation-competitions) are L2R problems on image data.

Or the Amazon/AIcrowd competitions (https://mlcontests.com/state-of-competitive-machine-learning-2022/#nlp--search) which were L2R with NLP.

In reality the mapping of competition:(competition type) is almost always one:many, and I'm planning on updating the ML Contests website to reflect that!

If I'd had more time and better data I would have sliced the data in multiple different ways to also look into e.g. L2R problems specifically in more depth.