PHP

function format_tree(&$result = [], $fid = 0) {
    $tree = [];

    if (is_array($result)) {
        foreach ($result as $v) {
            if ($v['fid'] == $fid) {
                $children = format_tree($result, $v['id']);
                if ($children) {
                    $v['sub'] = $children;
                }
                $tree[] = $v;
            }
        }
    }
    return $tree;
}

golang

type Leaf struct{
      Id int
      Pid int
      Deep int
      Name string
}

type Tree struck{
      Leaf 
      Children []Tree
}
//无限级分类树
func getTree(data []Leaf, pid int, level int) (ret []Tree) {
    for _, item := range data {
        if item.Pid == pid {
            item.Deep = level
            tmp := Tree{Leaf : item}
            //data=append(data[:i],data[i+1:]...)
            tmp.Children = getTree(data, item.Id, level+1)
            if len(tmp.Children) == 0 {
                tmp.Children = make([]Tree, 0)
            }
            ret = append(ret, tmp)
        }
    }
    return
}

golang的另外一个版本

import (
    "fmt"   
)

type Tree struct {
    Id       int    `json:"id,omitempty"`
    Pid      int    `json:"pid,omitempty"`
    Name     string `json:"name,omitempty"`
    Children []Tree `json:"children,omitempty"`
}

func main() {
    list := []Tree{
        {Id: 1, Name: "a1"},
        {Id: 2, Pid: 1, Name: "a2"},
        {Id: 3, Pid: 2, Name: "a3"},
        {Id: 4, Pid: 3, Name: "a4"},
        {Id: 5, Pid: 0, Name: "a5"},
        {Id: 6, Pid: 5, Name: "a6"},
    }
    var tree []Tree
    for _, v := range list {
        if v.Pid == 0 {                       
            v.Children = ChildrenTree(&list, v.Id) //树型         
            //v.Children = ChildrenList(&list, v.Id)//列表型
            tree = append(tree, v)
        }
    }
    str, _ := JsonEncode(tree)
    fmt.Printf("tree:%s\n", str)

}

// 子级：树型
func ChildrenTree(list *[]Tree, pid int) (children []Tree) {
    children = make([]Tree, 0)
    for i := 0; i < len(*list); i++ {
        if (*list)[i].Pid == pid {
            (*list)[i].Children = ChildrenTree(list, (*list)[i].Id)
            children = append(children, (*list)[i])
        }
    }
    return
}

// 子级：列表型
func ChildrenList(list *[]Tree, pid int) (children []Tree) {
    children = make([]Tree, 0)
    for i := 0; i < len(*list); i++ {
        if (*list)[i].Pid == pid {
            children = append(children, (*list)[i])
            children = append(children, ChildrenList(list, (*list)[i].Id)...)
        }
    }
    return
}


func JsonEncode(v interface{}) (string, error) {
    bytes, err := json.Marshal(v)
    if err != nil {
        return "", err
    }
    return string(bytes), nil
}

输出结果：

[
    {
        "id": 1,
        "name": "a1",
        "children": [
            {
                "id": 2,
                "pid": 1,
                "name": "a2"
            },
            {
                "id": 3,
                "pid": 2,
                "name": "a3"
            },
            {
                "id": 4,
                "pid": 3,
                "name": "a4"
            }
        ]
    },
    {
        "id": 5,
        "name": "a5",
        "children": [
            {
                "id": 6,
                "pid": 5,
                "name": "a6"
            }
        ]
    }
]