Walker::get_number_of_root_elements( array $elements )

	public function get_number_of_root_elements( $elements ){
		$num = 0;
		$parent_field = $this->db_fields['parent'];

		foreach ( $elements as $e) {
			if ( 0 == $e->$parent_field )
				$num++;
		}
		return $num;
	}