php无限级分类
CI的seven给我提供了一个方法，如下：
<?php /**
* 此方法由@Tonton 提供
* http://my.oschina.net/u/918697
* @date 2012-12-12
*/
function genTree5($items) {
foreach ($items as $item)
$items[$item['pid']]['son'][$item['id']] = &$items[$item['id']];
return isset($items[0]['son']) ? $items[0]['son'] : array();
}
/**
* 将数据格式化成树形结构
* @author Xuefen.Tong
* @param array $items
* @return array
*/
function genTree9($items) {
$tree = array(); //格式化好的树
foreach ($items as $item)
if (isset($items[$item['pid']]))
$items[$item['pid']]['son'][] = &$items[$item['id']];
else
$tree[] = &$items[$item['id']];
return $tree;
}
$items = array(
1 => array('id' => 1, 'pid' => 0, 'name' => '江西省'),
2 => array('id' => 2, 'pid' => 0, 'name' => '黑龙江省'),
3 => array('id' => 3, 'pid' => 1, 'name' => '南昌市'),
4 => array('id' => 4, 'pid' => 2, 'name' => '哈尔滨市'),
5 => array('id' => 5, 'pid' => 2, 'name' => '鸡西市'),
6 => array('id' => 6, 'pid' => 4, 'name' => '香坊区'),
7 => array('id' => 7, 'pid' => 4, 'name' => '南岗区'),
8 => array('id' => 8, 'pid' => 6, 'name' => '和兴路'),
9 => array('id' => 9, 'pid' => 7, 'name' => '西大直街'),
10 => array('id' => 10, 'pid' => 8, 'name' => '东北林业大学'),
11 => array('id' => 11, 'pid' => 9, 'name' => '哈尔滨工业大学'),
12 => array('id' => 12, 'pid' => 8, 'name' => '哈尔滨师范大学'),
13 => array('id' => 13, 'pid' => 1, 'name' => '赣州市'),
14 => array('id' => 14, 'pid' => 13, 'name' => '赣县'),
15 => array('id' => 15, 'pid' => 13, 'name' => '于都县'),
16 => array('id' => 16, 'pid' => 14, 'name' => '茅店镇'),
17 => array('id' => 17, 'pid' => 14, 'name' => '大田乡'),
18 => array('id' => 18, 'pid' => 16, 'name' => '义源村'),
19 => array('id' => 19, 'pid' => 16, 'name' => '上坝村'),
);
echo "<pre class="brush:php;toolbar:false">";
print_r(genTree5($items));
print_r(genTree9($items));
//后者输出格式，前者类似，只是数组键值不一样，不过不影响数据结构
/*
Array
(
[0] => Array
(
[id] => 1
[pid] => 0
[name] => 江西省
[son] => Array
(
[0] => Array
(
[id] => 3
[pid] => 1
[name] => 南昌市
)
[1] => Array
(
[id] => 13
[pid] => 1
[name] => 赣州市
[son] => Array
(
[0] => Array
(
[id] => 14
[pid] => 13
[name] => 赣县
[son] => Array
(
[0] => Array
(
[id] => 16
[pid] => 14
[name] => 茅店镇
[son] => Array
(
[0] => Array
(
[id] => 18
[pid] => 16
[name] => 义源村
)
[1] => Array
(
[id] => 19
[pid] => 16
[name] => 上坝村
)
)
)
[1] => Array
(
[id] => 17
[pid] => 14
[name] => 大田乡
)
)
)
[1] => Array
(
[id] => 15
[pid] => 13
[name] => 于都县
)
)
)
)
)
[1] => Array
(
[id] => 2
[pid] => 0
[name] => 黑龙江省
[son] => Array
(
[0] => Array
(
[id] => 4
[pid] => 2
[name] => 哈尔滨市
[son] => Array
(
[0] => Array
(
[id] => 6
[pid] => 4
[name] => 香坊区
[son] => Array
(
[0] => Array
(
[id] => 8
[pid] => 6
[name] => 和兴路
[son] => Array
(
[0] => Array
(
[id] => 10
[pid] => 8
[name] =>
东北林业大学
)
[1] => Array
(
[id] => 12
[pid] => 8
[name] =>
哈尔滨师范大学
)
)
)
)
)
[1] => Array
(
[id] => 7
[pid] => 4
[name] => 南岗区
[son] => Array
(
[0] => Array
(
[id] => 9
[pid] => 7
[name] => 西大直街
[son] => Array
(
[0] => Array
(
[id] => 11
[pid] => 9
[name] =>
哈尔滨工业大学
)
)
)
)
)
)
)
[1] => Array
(
[id] => 5
[pid] => 2
[name] => 鸡西市
)
)
)
)*通过测试，能够完成所设想的分类无限级，但是，用他自有数据可以，但是用我数据库的数据不可以,会出现错误，比如会出现如下错误：
Array
(
[10] => Array
(
[child] => Array
(
[14] =>
)
)
[11] =>
[12] =>
[9] => Array
(
[child] => Array
(
[13] =>
)
)
)只显示数组序号，不显示相应数据，这是我很苦恼，这样测试后能够完全显示：
function genTree5($items) {
foreach ($items as $item) {
$items[$item['id']]=$item;//ADD THIS
$items[$item['pid']]['son'][$item['id']] = &$items[$item['id']];
}
return isset($items[0]['son']) ? $items[0]['son'] : array();
} 但是这只在id升序状态下可以使用，乱序会显示错误
虽然在大多情况下id会保持升序状态，但是如果涉及到排序后，遍无法使用了。
之前，CI的吕老师提供了一种高效方法，即：
id 父id 分级 1 0 0，1 2 1 0，1，2 3 1 0，1，3 4 3 0，1，3，4 select * from 表 order by 分级 asc
这个结构，会使分级按照父子顺序排序，首先对第一个0排序，然后对第二个1排序，以此类推，自动分类，十分好用（同时注意，一定要保持有两组，也就是0，1开始或者0，0开始，否则根分级会提前显示）。“分级”也可以叫childid,因为是记录的子id层。
|--2 |----2-1 |------2-1-1 |--3 |----3-1 |--4 |--1 |----1-1显示直接遍历即可，因为我有一个depth字段，记录深度，所以能更好的显示。
这个方法运行时间也较短，微秒级运行，总之耗费在数据库排序上了，其他的基本很愉快。
利用指针的一般在没有缓存情况下测试大多数大于排序后的时间，大多数是CPU时间，而且，结果不准确。
PS:PHP已经对地址，指针之类的概念弱化了，也就是说，并不是PHP的特点，虽然可以使用，但是会出现一些莫名错误。所以还是老老实实的吧~神马大数据算法，就不用PHP来做了，C++什么的，干这个，比PHP速度快多了。。。。
同时 @Tonton 对他的算法进行修正。
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