[WP] the_category(): display only parents

/* https://ja.wordpress.org/support/topic/ループ内で、親と子カテゴリーを選択したとき、/ */
function my_category_list( $categories, $post_id ) {
    $cats = $categories;
    $cats_ID = array_map( function ( $cat ) {
        return $cat->term_id;
    }, $cats );
    foreach ( $categories as $key => $category ) {
        $ancestor = $category;
        while ( ! empty( $ancestor->parent ) && $ancestor = get_category( $ancestor->parent ) ) {
            if ( in_array( $ancestor->term_id, $cats_ID, true ) ) {
                unset( $cats[ $key ] );
                break;
            }
        }
    }
    return $cats;
}
add_filter( 'the_category_list', 'my_category_list', 10, 2 );