How do I count how many top level categories there are?

As the Codex says, this is the code block to query for only the Top Label categories — the parents. With this, I used the PHP function count().

<?php    
$args = array(
  'parent' => 0,
  'hide_empty' => 0
  );

$categories = get_categories( $args );

echo count( $categories );    
?>