Скачать или смотреть How to Return a List of Users with Common Tags in Prolog

Learn how to return a list of users with common tags in `Prolog`. This guide provides a step-by-step explanation for efficiently filtering users based on a mandatory tag and shared interests.
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How to Return a List of Users with Common Tags in Prolog

Navigating user data in Prolog can be a bit tricky, especially when you need to filter users based on shared interests and mandatory tags. If you've got a scenario where you want to list users who share specific tags with a given user, but at least one tag must be present, you've come to the right place. In this post, we'll walk through how to set up your knowledge base and write a Prolog predicate to achieve this.

Understanding the Problem

You want to return a list of users who:

Share a specified number of tags with a current user,

Have at least one mandatory tag in common with that user.

Example Scenario

Consider the following knowledge base where we have users defined by their IDs, names, and a list of tags associated with each user:

[[See Video to Reveal this Text or Code Snippet]]

If you ask Prolog:

?- suggest_group(ana, 3, cat, LGroup).

The expected result is LGroup = [], meaning no group of 3 users satisfies the criteria.

If you ask instead:

?- suggest_group(ana, 2, cat, LGroup).

You should get LGroup = [antonio, isabel] since both share the mandatory tag cat with user ana.

Implementing the Solution

The following predicate will help achieve your goal. Let's explain the suggest_group predicate step by step.

Code Breakdown

[[See Video to Reveal this Text or Code Snippet]]

Findall: This part extracts all users except the current one while ensuring that they have the mandatory tag. The result is stored in Zs.

Collapse: The helper predicate collapse combines the tags of the users found into a single list while ensuring the intersection of their tags. If the length of the resulting list matches the requested number of users, it's returned. Otherwise, an empty list is returned.

Helper Function: Collapse

Here's how the collapse function operates:

[[See Video to Reveal this Text or Code Snippet]]

Base Case: When there's only one user and their tags, we simply return them.

Recursive Case: It combines the tags of multiple users while calculating their intersections, filtering the list.

Testing the Predicate

This is how you would use the implementation in a Prolog query:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

In this guide, we explored how to construct a Prolog predicate that allows you to retrieve users with specific mandatory tags while meeting specified criteria. By breaking down the logic and leveraging findall and recursive functions, we can efficiently filter through our knowledge base.

Now you can apply this method to any similar problem involving tag-based user filtering in Prolog. Keep experimenting and enhancing your Prolog skills!