WordPress: Combine two loops with different amount of posts - php

Question

I want to show a random selection of 4 new products in WooCommerce.
For that I'm using a first loop to get the 20 newest products.
Like this:
$args= array(
'post_type' => 'product',
'posts_per_page' => 20,
'orderby' => 'date',
);
Now I've a second loop to reduce the products to 4 in a random order:
$args_new = array(
'posts_per_page' => 4,
'orderby' => 'rand',
);
In the end I merge the two loops:
$final_args = array_merge( $args, $args_new );
But that doesn't work. Is there any other way to achieve it?

Answer 1

General knowledge
The post_type argument accept String or Array.
Argument
Description
post_type
(String/Array) – use post types. Retrieves posts by post types, default value is post. If tax_query is set for a query, the default value becomes any.
Source # https://developer.wordpress.org/reference/classes/wp_query/#post-type-parameters
Merging queries
In crude terms we want to combine 2 posts queries, retrieve each posts ID, push them to a new array and open a new query.
Keep in mind that if you want your 4 posts to be random (as you stated in the comments) they might be some duplicates of the last 20 from the first query. Don't forget to offset the second query.
<?php
// First query
$args_1 = get_posts( array(
'post_type' => 'dogs',
'post_status' => 'publish',
'post_count' => 20,
) );
// Second query
$args_2 = get_posts( array(
'post_type' => 'dogs',
'post_status' => 'publish',
'post_count' => 4,
'offset' => 20,
'orderby' => RAND,
) );
// Merge queries
$posts = array_merge( $args_1, $args_2 );
// Push posts IDs to new array
$identifiers = array();
foreach ( $posts as $post ) {
array_push( $identifiers, $post->ID );
};
// Third query
$query = new WP_Query( array(
'post_status' => 'publish',
'post_count' => 24,
'post_in' => array_unique( $identifiers ),
) );
var_dump( $query );