Exclude posts with certain tags in category archive

Question

When we click a category link we find all posts under that category. I would like to hide posts from specific tag within that category, and to show a link which enable us to show the posts on that tag (which was hidden) within category. With jQuery and tabs I can achieve this, but there is a problem with pagination. So I need to find another way.

Example: We have 10 posts; 5 with Category A and 5 with Category B.

Of those, 3 posts have Tag C (2 from Category A and 1 from Category B).

When I click category A will show 3 posts (hidding the two tagged 'C') and afterwards (when I'm in category page) if I click Tag C it will show 2 posts (not 3, because 1 post has category B).

Is this possible?

Answer 1

You could modify your query on pre_get_posts.

Example:

// I'd wouldn't hardcode the tags/category ids, but where to store and 
// how to retrieve those settings go beyond the scope of this question.

define( 'YIVIS_EXCLUDED_TAG', 12 );

add_action( 'pre_get_posts', 'yivi_excludes_tags' ); 

function yivi_excludes_tags( $query ) {

  if ( $query->is_category() {
     $query->set('tag', [ YIVIS_EXCLUDED_TAG *  -1 ] );
  }

}

With this, every time you are performing a category based query posts tagged with that tag would be excluded from the search. To exclude certain categories on a tag view should be easy enough going on from here.