The ability to get book recommendations

[nightgolfer]

Is your feature request related to a problem? Please describe.

I really wish there was a way to get recommendations on BookWyrm. For me personally, logging my reads and to-reads in a database is 90% about finding other books that I might like.

Describe the solution you'd like

I would like a "Recommendations" section in Discover. When clicked, BookWyrm would suggest books I might like to read, based on books I've read, and how those books intersect with lists of books other people have read.

I don't think a super complicated algorithm is needed, although I'm not quite qualified to gauge the issue. My thought for a simple implementation is something like this:

• Sort my Read Books List by My Rating as List W.
• Select top 5 books from List W, sort by Book Rating, as List W¹.
• Book X is the top book in List W¹, and is classified as being in Category X.
• Find Book X in other libraries as List X.
• (if data available, sort List X by some sort of metric, e.g. amount of list Likes).
• Select top list in List X as List Y.
• Look at other books in List Y, select any that are in Category X. This is List Z.
• Sort List Z by Book Rating, return top 5 books as Recommendations.

Describe alternatives you've considered

The ability to find books similar to a given book (basically, a "Similar Books" button on any book page), although I do not know what the metric would be, other than some sort of feature that let people tag a book with "This book reminds me of this other book:".

I spend a lot of time logging my reading activity, and would be very thrilled if the data that comes from that could benefit me in some way. If that's not something BookWyrm is into, I've considered that it might just be a bad fit for me. Was very excited about the Federated aspect of it all, and the prospect of leaving GoodReads (and Amazon) behind, but I'm not seeing that happening without recommendations.

Additional context

[hughrun]

This is really useful input to #2751

[j6k4m8]

A super simple version is recommending books from shelves of other users with whom you have a lot of other overlapping books — doesn't require hitting ratings tables at all, which keeps it computationally cheap. (Feels like this shouldn't work, but it tends to converge on correct!)
I was thinking about doing this with #785, maybe #3361 enables multiple recommender apps to live alongside without needing to go in this repo!