Hi. I would like to display user most active category in his user profile.
Is this possible ?
It's certainly possible. But there is one catch I see here: category permissions. Imagine you have a forum where you have a category which is reserved for admins and mods. Or any other category which isn't public, a category which is only accessible for forum members. What should a guest see when he is looking at the profile of a user who is most active in a non public category?
Most probably the second most used category, okay. But the problem is, that in such a case a) you would have to calculatate the information for each profile visit or b) cache more values.
But further than that, I couldn't see a real problem here.
Depending on where in the profile you like to see that information and how, you might me able to "re-use" an existing plugin to solve the problem on how to show something in the profile.
Normally I advice to use a model to get information from tables. In this case I would advice to use a prepared SQL query, since it would be quite complicated.
I would store the result (a sorted array of categories) in the UserMeta table and recalculate the information
I don't think this is a good beginner plugin, but if you have some programming experiences, it's surely do-able.