Get the latest child category/ies (those who aren't parent) for a specific post

get-last-children-taxonomies-for-post.php

<?php
/**
 * Get the latest hierarchical taxonomy children of a post
 *
 * @author  Mauricio Gelves <[email protected]>
 * @param	$post_id  int Post ID
 * @return  array
 */
function get_last_children_taxonomy_in_post( $post_id, $taxonomy = 'category'){

    // Parameter check
    if( empty($post_id) || !is_numeric($post_id) ) return false;
    
    //Get all terms associated with post in a hierarchical taxonomy (default 'category')
    $terms = get_the_terms( $post_id, $taxonomy );

    //Get an array of their IDs
    $term_ids = wp_list_pluck( $terms,'term_id' );

    //Get array of parents - 0 is not a parent
    $parents = array_filter( wp_list_pluck( $terms, 'parent' ) );

    //Get array of IDs of terms which are not parents.
    $term_ids_last_child = array_diff( $term_ids,  $parents );

    //Get corresponding term objects
    $terms_not_parents = array_intersect_key( $terms,  $term_ids_last_child );

    return $terms_not_parents;

}



/**
 * Get latest children category/ies of a post
 *
 * @author  Mauricio Gelves <[email protected]>
 * @param	$post_id  int Post ID
 * @return  array
 */
function get_last_children_categories($post_id){
    
    // Parameter check
    if( empty($post_id) || !is_numeric($post_id) ) return false;
    
    return get_last_children_taxonomy_in_post( $post_id );
    
}