递归无限级分类有几种形式，我这里仅仅举例比較经常使用的三种：
第一种：返回有排序的数组：
<?php$data = array(1 => array('id' => 1,'pid' => 0,'user_name' => 'one',),2 => array('id' => 2,'pid' => 1,'user_name' => 'two',),3 => array('id' => 3,'pid' => 1,'user_name' => 'two',),4 => array('id' => 4,'pid' => 2,'user_name' => 'three',),5 => array('id' => 5,'pid' => 2,'user_name' => 'three',),6 => array('id' => 6,'pid' => 5,'user_name' => 'four',),
);function genCate( $data, $pid = 0, $level = 0 ) {static $result = array();$result = ($level == 0) ? array() : $result;$prefix = ($level == 0) ? '' : str_repeat( '-', $level );foreach ( $data as $key => $row ) {if ( $row['pid'] == $pid ) {$row['user_name'] = $prefix . $row['user_name'];$result[] = $row['user_name'];genCate( $data, $row['id'], $level + 1 );}}return $result;
}echo '<pre>';
$result = genCate( $data );
print_r( $result );
exit;
?>另外一种：返回html字符串形式：
function getTreeHtml( $data, $pId ) {$html = '';foreach ( $data as $k => $v ) {if ( $v['pid'] == $pId ) { $html .= "<li>" . $v['user_name'];$html .= getTree( $data, $v['id'] );$html = $html . "</li>";}}return $html ? '<ul>' . $html . '</ul>' : $html;
}第三种：返回多维数组形式：
function getTreeArray( $data, $pId = 0 ) {$tree = array();foreach ( $data as $key => $value ) {if ( $value['pid'] == $pId ) {$value['childrens'] = getTreeArray( $data, $value['id'] );$tree[] = $value;}}return $tree;
}
