How would I use derivatives for suggesting an option to my user?

Question

I was learning derivatives. I understood the theoretical concept behind it. When I was searching for the real-life example in machine learning I came across one of the answers in this question How do we use derivatives in our daily lives.

Gist is : If netflix has to suggest a movie to a user, then it will check which of the movies he has liked and based on the ratings of those movies, the algorithm will try to find the movie closes to that range.

I have tried (my best) to understand this but failed to find out how exactly the math behind it would go.

So I want your help to solve this concrete example :

Suppose I have a user x and he has liked or upvoted movies with star rating 5,6,8,3 and has disliked movies with remaining values. (I am considering domain of stars is in the range 0-10).

Now how would I use derivatives to solve this problem ?

Thanks in advance :)

If its a very stupid question, atleast let me know why :)

Answer 1

If a person $x$ likes a movie with a certain rating $y$, it doesn't imply he that likes all movies with rating $y$. The only use of the derivative would be to find how fast he is changing his taste from low rating movies to higher ones or vice versa at a certain moment, but the function wouldn't be continuous so you'd have to interpolate a polynomial and find its derivative instead. But it is completely useless.