separate_comments( WP_Comment[] $comments )

function separate_comments(&$comments) {
	$comments_by_type = array('comment' => array(), 'trackback' => array(), 'pingback' => array(), 'pings' => array());
	$count = count($comments);
	for ( $i = 0; $i < $count; $i++ ) {
		$type = $comments[$i]->comment_type;
		if ( empty($type) )
			$type = 'comment';
		$comments_by_type[$type][] = &$comments[$i];
		if ( 'trackback' == $type || 'pingback' == $type )
			$comments_by_type['pings'][] = &$comments[$i];
	}

	return $comments_by_type;
}