Build Releated Posts Array in WordPress

related-posts.php

<?php
/**
 * Build a posts array, used for related posts.
 *
 * - It grabs a random number of posts up to $limit with the same $taxonomy and same $post_type as $post_id
 *   And if you haven't hit the limit, then gets random posts.
 *
 * - To use this, refer to the code to the bottom
 *
 * @param  integer $post_id   The integer of the amount posts we have
 * @param  mixed   $taxonomy  The taxonomy we're using, or false if not present
 * @param  mixed   $post_type The post type string or array we're using
 * @param  integer $limit     The number of posts to return
 * @return array
 */
function dwinrhys_build_related_posts_array($post_id, $taxonomy = false, $post_type = 'post', $limit = 3)
{

	$exclude  = array($post_id);
	$post_ids = array();


	if ($taxonomy) {

		$term_obj_list = get_the_terms($post_id, $taxonomy);


		if (!empty($term_obj_list) && !is_wp_error($term_obj_list)) {
			$termnames = wp_list_pluck($term_obj_list, 'name');
		}

		if ($termnames) {

			$firstpass = new WP_Query(
				array(
					'post_type'      => $post_type,
					'post__not_in'   => $exclude,
					'orderby'        => 'rand',
					'posts_per_page' => $limit,
					'tax_query' => array(
						array(
							'taxonomy' => $taxonomy,
							'field'    => 'name',
							'terms'    => $termnames
						)
					),
				)
			);

			if ($firstpass->have_posts()) {
				while ($firstpass->have_posts()) {
					$firstpass->the_post();
					$post_ids[] = get_the_ID();
					$exclude[]  = get_the_ID();
				}
			}

			wp_reset_postdata();
		}
	}

	// If we don't have enough, lets return more general posts
	if (count($post_ids) < $limit) {
		$secondpass = new WP_Query(
			array(
				'post_type'      => $post_type,
				'post__not_in'   => $exclude,
				'orderby'        => 'rand',
				'posts_per_page' => $limit
			)
		);

		if ($secondpass->have_posts()) {
			while ($secondpass->have_posts()) {
				$secondpass->the_post();
				$post_ids[] = get_the_ID();
			}
		}

		wp_reset_postdata();
	}

	$post_ids_to_return = array_slice($post_ids, 0, $limit);

	return $post_ids_to_return;
}

// Get three of the latest posts from the same category as the current post
 $related_posts = dwinrhys_build_related_posts_array( get_the_id(), 'category' );
// You need to do this
 global $post;

foreach ($related_posts as $post) {
   get_post($post);
   
   // Do the display code here
}

wp_reset_postdata();