摘要：分層數(shù)據(jù)探索例如無限級分類多級菜單省份城市引言什么是分層數(shù)據(jù)類似于樹形結(jié)構(gòu)，除了根節(jié)點和葉子節(jié)點外，所有節(jié)點都有一個父節(jié)點和一個或多個子節(jié)點。接下來我會先通過一般方法和遞歸方法來實現(xiàn)無限極分類，然后再通過兩種數(shù)據(jù)模型來談一談分層數(shù)據(jù)的處理。

什么是分層數(shù)據(jù)？

類似于樹形結(jié)構(gòu)，除了根節(jié)點和葉子節(jié)點外，所有節(jié)點都有一個父節(jié)點和一個或多個子節(jié)點。

大多數(shù)同學都曾在數(shù)據(jù)庫中處理過分層數(shù)據(jù)(hierarchical data)，分層數(shù)據(jù)存在于許多基于數(shù)據(jù)庫的應(yīng)用程序中，包括論壇和郵件列表中的分類、商業(yè)組織圖表、內(nèi)容管理系統(tǒng)的分類、產(chǎn)品分類、無限級分類、多級菜單、省份城市等等。但是因為關(guān)系數(shù)據(jù)庫中的表沒有層次關(guān)系，只是簡單的平面化的列表；而分層數(shù)據(jù)具有父－子關(guān)系，顯然關(guān)系數(shù)據(jù)庫中的表不能自然地表現(xiàn)出其分層的特性。

接下來我會先通過一般方法和遞歸(recursion)方法來實現(xiàn)無限極分類，然后再通過兩種數(shù)據(jù)模型來談一談分層數(shù)據(jù)的處理。

分層數(shù)據(jù)Hierarchical Data探索(1.遞歸 recursion)

分層數(shù)據(jù)Hierarchical Data探索(2.鄰接表模型 Adjacency List Model)

分層數(shù)據(jù)Hierarchical Data探索(3.嵌套集合模型 Nested Set Model)

& 引用賦值

function doloop1(&$i = 1)
{
    print_r($i);
    $i++;
    if ($i <= 10) {
        doloop1($i);
    }
}
doloop1();

static 靜態(tài)變量

function doloop2()
{
    static $i = 1;
    print_r($i);
    $i++;
    if ($i <= 10) {
        doloop2();
    }
}

doloop2();

global 全局變量

$i = 1;
function doloop3()
{
    global $i;
    echo $i;
    $i++;
    if ($i <= 10) {
        doloop3();
    }
}
doloop3();

# 模擬數(shù)據(jù)
       $data = [
            ["id" => 1, "title" => "Electronics", "parent_id" => 0],
            ["id" => 2, "title" => "Laptops & PC", "parent_id" => 1],
            ["id" => 3, "title" => "Laptops", "parent_id" => 2],
            ["id" => 4, "title" => "PC", "parent_id" => 2],
            ["id" => 5, "title" => "Cameras & photo", "parent_id" => 1],
            ["id" => 6, "title" => "Camera", "parent_id" => 5],
            ["id" => 7, "title" => "Phones & Accessories", "parent_id" => 1],
            ["id" => 8, "title" => "Smartphones", "parent_id" => 7],
            ["id" => 9, "title" => "Android", "parent_id" => 8],
            ["id" => 10, "title" => "iOS", "parent_id" => 8],
            ["id" => 11, "title" => "Other Smartphones", "parent_id" => 8],
            ["id" => 12, "title" => "Batteries", "parent_id" => 7],
            ["id" => 13, "title" => "Headsets", "parent_id" => 7],
            ["id" => 14, "title" => "Screen Protectors", "parent_id" => 7],
        ];

/**
 * 值引用獲取無限極分類樹
 * 
 * @param array $data
 * @return array
 */
function make_tree($data)
{  
    $refer = array();  
    $tree = array();  
    foreach($data as $k => $v){  
        $refer[$v["id"]] = & $data[$k];  //創(chuàng)建主鍵的數(shù)組引用  
    }  

    foreach($data as $k => $v){  
        $parent_id = $v["parent_id"];   //獲取當前分類的父級id  
        if($parent_id == 0){  
            $tree[] = & $data[$k];   //頂級欄目
        }else{  
            if(isset($refer[$parent_id])){  
                $refer[$parent_id]["children"][] = & $data[$k];  //如果存在父級欄目，則添加進父級欄目的子欄目數(shù)組中  
            }  
        }  
    }  

    return $tree;  
}

/**
 * 遞歸獲取無限極分類樹
 * 
 * @param array $data
 * @param int $parent_id
 * @param int $level
 * @return array
 */
function make_tree2($data = [], $parent_id = 0, $level = 0)
{
    $tree = [];
    if ($data && is_array($data)) {
        foreach ($data as $v) {
            if ($v["parent_id"] == $parent_id) {
                $tree[] = [
                    "id" => $v["id"],
                    "level" => $level,
                    "title" => $v["title"],
                    "parent_id" => $v["parent_id"],
                    "children" => make_tree2($data, $v["id"], $level + 1),
                ];
            }
        }
    }
    return $tree;
}

/**
 * 引用賦值方式
 * @param array $data
 * @param int $id
 * @param int $level
 * @return array
 */
function getSubTree($data = [], $id = 0, $level = 0)
{
    static $tree = [];

    foreach ($data as $key => $value) {
        if ($value["parent_id"] == $id) {
            $value["laravel"] = $level;
            $tree[] = $value;
            getSubTree($data, $value["id"], $level + 1);
        }
    }
    return $tree;
}

/**
 * 靜態(tài)變量方式
 * @param array $data
 * @param int $id
 * @param int $level
 * @return array
 */
function getSubTree($data = [], $id = 0, $level = 0)
{
    static $tree = [];

    foreach ($data as $key => $value) {
        if ($value["parent_id"] == $id) {
            $value["laravel"] = $level;
            $tree[] = $value;
            getSubTree($data, $value["id"], $level + 1);
        }
    }
    return $tree;
}


/**
 * 全局變量方式
 * @param array $data
 * @param int $id
 * @param int $level
 * @return array
 */

$tree = [];  //先申明變量
function getSubTree($data = [], $id = 0, $level = 0)
{
    global $tree;

    foreach ($data as $key => $value) {
        if ($value["parent_id"] == $id) {
            $value["laravel"] = $level;
            $tree[] = $value;
            getSubTree($data, $value["id"], $level + 1);
        }
    }
    return $tree;
}

/**
 * getParentsByParentId2($categories, 9)
 *
 * @param array $data
 * @param $parent_id
 * @return array
 */
function getParentsByParentId($data = [], $parent_id)
{
    static $categories = [];

    if ($data && is_array($data)) {
        foreach ($data as $item) {
            if ($item["id"] == $parent_id) {
                $categories[] = $item;
                getParentsByParentId($data, $item["parent_id"]);
            }
        }
    }
    return $categories;
}

function getParentsByParentId2($data = [], $parent_id)
{
    $categories = [];

    if ($data && is_array($data)) {
        foreach ($data as $item) {
            if ($item["id"] == $parent_id) {
                $categories[] = $item;
                $categories = array_merge($categories, getParentsByParentId2($data, $item["parent_id"]));
            }
        }
    }
    return $categories;
}