display related product of same subcategory in woocommerce

Modify related.php template file. PATH: your-theme/woocommerce/single-product/related.php


Change $args to,

$args = apply_filters( 'woocommerce_related_products_args', array(
    'post_type' => 'product',
    'ignore_sticky_posts' => 1,
    'no_found_rows' => 1,
    'posts_per_page' => $posts_per_page,
    'orderby' => $orderby,
    'post__not_in' => array( $product->id ),
    'tax_query' => array(
        array(
            'taxonomy' => 'product_cat',
            'field' => 'id',
            'terms' => $cats_array
        ),
    )
) );

where $cats_array is,

$cats_array = array(0);
// Get product categories
$terms = wp_get_post_terms( $product->id, 'product_cat' );

//Select only the category which doesn't have any children
if( sizeof( $terms ) ){
    foreach ( $terms as $term ) {
        $children = get_term_children( $term->term_id, 'product_cat' );
        if ( !sizeof( $children ) )
            $cats_array[] = $term->term_id;
    }
}

and remove/comment following lines,

$related = $product->get_related( $posts_per_page );
if ( sizeof( $related ) == 0 ) return;

 original