Exclude parent categories from recent posts list

Question

I want to show only the sub-categories from a post's specific parent category and exclude all the other categories.

This is for a loop of recent posts on my front-page.php. Each recent post is currently listing its categories using get_the_category_list($post->ID).

I tried get_the_category_list($parent, '8') but it didn't exclude anything. 8 is the integer of the parent category I want to keep. Any help is much appreciated!

Here's my code:

<?php $the_query = new WP_Query(array(
    'post_type'      => 'post',
    'category_name'  => 'genres',
    'posts_per_page' => 6,
    'post_status'    => 'publish'
    ));

    while ( $the_query->have_posts() ) : $the_query->the_post();

        echo '<div class="wrapper">
            <div> // stuff with post title, image and excerpt </div> 
            <div>' . get_the_category_list( $post->ID ) . '</div>';

    endwhile;
    wp_reset_postdata(); ?>

I want to go from this:

Parent-category 1, Sub-category 1 , Parent-category 2, Sub-category 2, Parent-category 3, Sub-category 3

To this:

Sub-category 1

Answer 1

I was able to find a function that worked found here.

First, I added the below code to my functions.php, which excludes the parent categories I do not want:

function custom_get_the_category_list() {
    $categories = get_the_category();
    $exclude1 = get_cat_ID( 'Parent1' );
    $exclude2 = get_cat_ID( 'Parent2' );
    $categories_list = '';

    foreach ( $categories as $category ) {
        if ( $category->category_parent == $exclude1
                || $category->cat_ID == $exclude1 || $category->category_parent == $exclude2
                || $category->cat_ID == $exclude2  ) {
            continue;
        }
        $categories_list .=
            '<li><a href="' . get_category_link( $category->cat_ID ) . '">' .
            $category->name .
            '</a></li>';
    }

    return '<ul class="post-categories">' . $categories_list . '</ul>';
}

And then in my loop, instead of using get_the_category_list($post->ID), I used the new function custom_get_the_category_list().

It certainly works, but if anyone finds a simpler solution please post.