Snippet to show only products from same subcategory in Related Products grid on WooCommerce product page

subcategory-related-products.php

<?php

add_filter('woocommerce_related_products', 'filter_related_products', 9999, 3);
function filter_related_products( $related_posts, $product_id, $args ) {
	$subCategories = array();	
	$terms = get_the_terms( $product_id, 'product_cat' );
	
	// select only the category which doesn't have any children
	foreach ( $terms as $term ) {
		$children = get_term_children( $term->term_id, 'product_cat' );
		if ( !sizeof( $children ) )
			$subCategories[] = $term->term_id;
	}
	
	if ( $subCategories ) {			
		$args = array();		
		$args = get_posts( array(
		  'post_type' => 'product',
		  'exclude' => array( $product_id ),
		  'posts_per_page' => -1,
		  'tax_query' => array(
			array(
				'taxonomy' => 'product_cat',
				'field' => 'id',
				'terms' => $subCategories
			),
		  )
		));		
		return $args;
	} else {
		return $args;
	}
}

?>