display lists of categories an author has written a post in

Hello!
my website: ampersandbox.net/?author=2

Basically on every author’s page I would like to display a list on the right side of categories the current author has contributed to (has written a post in)

I’m not sure how to go about this but I started trying to write some code I came up with this code but for some reason it only displays one category which happens to be category 2. (check column on right labeled CATEGORIES)

<?php
//Gets category and author info
  global $wp_query;
$cats = get_the_category();
  $postAuthor = $wp_query->post->post_author;
$tempQuery = $wp_query;
// related category posts
  $catlist = "";
  forEach( $cats as $c ) {
  if( $catlist != "" ) { $catlist .= ","; }
  $catlist .= $c->name;
  $catlist .= $c->description;
  }
  $newQuery = "posts_per_page=5&cat=" . $catlist;
  query_posts( $newQuery );
$categoryPosts = "";
  $count = 0;
  ?>
<?php echo $catname .' '. $catlist; ?>