Show one post per author in WP

gistfile1.aw

add_filter('posts_groupby', 'author_groupby');

function author_groupby($groupby)
{
  global $wpdb;

  $author_groupby = "{$wpdb->posts}.post_author";

  if(preg_match("/$author_groupby/", $groupby)) {
    // grouping we need is already there
    return $groupby;
  }

  if(strlen(trim($groupby) == 0)) {
    // groupby was empty, use ours
    return $author_groupby;
  }

  return "$groupby, $author_groupby";
}