How to hide a child category and show his parent category

Question

i have the following schematic:

    the world
        - Cover the world.
    
    The country
        -Covered the country.
    
    theater
        - theater cover.

etc...

And I want that when I select any of the child categories the parent category appears.

my code:

add_filter('get_the_terms', 'hide_categories_terms', 10, 3);

function hide_categories_terms($terms, $post_id, $taxonomy){

    // define which category IDs you want to hide
    $excludeIDs = array(31, 32, 33, 34, 35, 36, 37, 38, 96);

    // get all the terms 
    $exclude = array();
    foreach ($excludeIDs as $id) {
        $exclude[] = get_term_by('id', $id, 'category');
    }

    // filter the categories
    if (!is_admin()) {
        foreach($terms as $key => $term){
            if($term->taxonomy == "category"){
                foreach ($exclude as $exKey => $exTerm) {
                    if($term->term_id == $exTerm->term_id) unset($terms[$key]);
                }
            }
        }
    }

    return $terms;
}

but just hide the child category.

Answer 1

This is what you want to achieve as I understand:

If a post is assigned to a child category, then remove it and show only its parent on the categories list of that post.

You can use the following code to achieve that for any child category:

add_filter('get_the_terms', function($terms, $postId, $taxonomy) {

    // Return early if not a category, there is an error, or we are on the dashboard.
    if('category' !== $taxonomy || is_wp_error($terms) || is_admin()) {
        return $terms;
    }

    // Create an array that will hold only parent categories
    $parents = [];

    // Loop on all the terms, keep the parents or get the parent of any child
    foreach ($terms as $term) {

        // This is a parent, add it and continue
        if(! $term->parent) {
            $parents[$term->term_id] = $term;
            continue;
        }

        // This is a child get its parent and add it
        $parent = get_term($term->parent, $taxonomy);
        if(is_a($parent, 'WP_Term')) {
            $parents[$parent->term_id] = $parent;
        }

    }

    // Finally, reset the array keys and return it
    return array_values($parents);

}, 10, 3);

But, if you want to do this for only a selected list of child categories, use this code:

add_filter('get_the_terms', function($terms, $postId, $taxonomy) {

    // Return early if not a category, there is an error, or we are on the dashboard.
    if('category' !== $taxonomy || is_wp_error($terms) || is_admin()) {
        return $terms;
    }

    // Categories to exclude
    $excludedIds = [31, 32, 33, 34, 35, 36, 37, 38, 96];

    // Create an array that will hold only not excluded categories
    $categoriesToKeep = [];

    // Loop on all the terms, and replace the excluded categories with their parents
    foreach ($terms as $term) {

        // This is not in the excluded list, add it and continue
        if(! in_array($term->term_id, $excludedIds)) {
            $categoriesToKeep[$term->term_id] = $term;
            continue;
        }

        // This an excluded category, replace it with its parent
        $parent = get_term($term->parent, $taxonomy);
        if(is_a($parent, 'WP_Term')) {
            $categoriesToKeep[$parent->term_id] = $parent;
        }

    }

    // Finally, reset the array keys and return it
    return array_values($categoriesToKeep);

}, 10, 3);