gistfile1.txt

$taxonomy = get_term( $category_id )->taxonomy;

// get all post IDs within selected category
$posts_in_category = new WP_Query( array(
  'fields' => 'ids',
  'tax_query' => array(
    array(
      'taxonomy' => $taxonomy,
      'terms'    => $category_id,
    ),
  )
) );

foreach( $posts_in_category->posts as $cat_post ) {
// get total votes for each post in category - update their postmeta
}