Category Archive, list subcategories of each post

Question

I found this post, but it was never answered. I'm looking for the same thing, haven't been able to find a solution so far.

My problem is that I can't find a way to list subcategories unique to each post on a category archive page. My markup is currently this:

<article <?php post_class( 'grid_item' ); ?>>
  <div class="grid_item--inner">
    <?php the_post_thumbnail(); ?>
    <header>
      <a class="cat_card--link" href="<?php the_permalink(); ?>">
        <h2 class="cat_card--title"><?php the_title(); ?></h2>
        <?php get_template_part('templates/entry-meta'); ?>
      </a>
    </header>
    <div class="cat_card--cats">
      <?php wp_list_categories('title_li=&style=none'); ?>
    </div>
  </div>
</article>

This of course will list all subcategories of the current page's category. Looking through the WP codex documentation, I haven't been able to find a way to list only the applicable subcategories of each post. Is this possible? If so, how do I achieve this?

EDIT: To clarify, I'm interested in listing each subcategory like so:

Parent Category: "Video"
  - Post 1: Subcategory "Comedy"
  - Post 2: Subcategory "Action"
  - Post 3: Subcategories "Comedy, Action"

Where each post only lists the subcategories it uses.

Answer 1

If you want to list only child categories of the current category, set the child_of argument to the current category ID.

wp_list_categories(
    array(
        'child_of' => get_queried_object_id(), // this will be ID of current category in a category archive
        'style' => 'none',
        'title_li' => ''
    )
);

EDIT- To list only child categories per-post of the current category, you'll need to filter the list of each post's terms to check that parent is the current category ID.

$terms = get_the_terms( get_the_ID(), 'category' );

if( $terms && ! is_wp_error( $terms ) ){
    echo '<ul>';
    foreach( $terms as $term ) {
        if( get_queried_object_id() == $term->parent ){
            echo '<li><a href="' . get_term_link( $term ) . '">' . $term->name . '</a></li>';
        }
    }
    echo '</ul>';
}