C# 生成层次结构的算法

Question

我有一个如下所示的文本文件：

{ Id = 1, ParentId = 0, Position = 0, Title = "root" }
{ Id = 2, ParentId = 1, Position = 0, Title = "child 1" }
{ Id = 3, ParentId = 1, Position = 1, Title = "child 2" }
{ Id = 4, ParentId = 1, Position = 2, Title = "child 3" }
{ Id = 5, ParentId = 4, Position = 0, Title = "grandchild 1" }

我正在寻找一个通用的 C# 算法，它将由此创建一个对象层次结构。如果您愿意的话，可以使用“层次化”功能，将这些数据转换为对象层次结构。

有任何想法吗？

编辑 我已经将文件解析为 .NET 对象：

class Node
{
    public int Id { get; }
    public int ParentId { get; }
    public int Position { get; }
    public string Title { get; }
}

现在我需要将对象实际排列到对象图中。

Answer 1

非常感谢乔恩和mquander - 是你们给了我足够的信息来帮助我在一个适当的，通用的方式解决这个问题。这是我的解决方案，其将对象转换成层次结构形式的单个通用扩展方法：

public static IEnumerable<Node<T>> Hierarchize<T, TKey, TOrderKey>(
    this IEnumerable<T> elements, 
    TKey topMostKey, 
    Func<T, TKey> keySelector, 
    Func<T, TKey> parentKeySelector, 
    Func<T, TOrderKey> orderingKeySelector)
{
    var families = elements.ToLookup(parentKeySelector);
    var childrenFetcher = default(Func<TKey, IEnumerable<Node<T>>>);
    childrenFetcher = parentId => families[parentId]
        .OrderBy(orderingKeySelector)
        .Select(x => new Node<T>(x, childrenFetcher(keySelector(x))));

    return childrenFetcher(topMostKey);
}

利用该小节点类：

public class Node<T>
{
    public T Value { get; private set; }
    public IList<Node<T>> Children { get; private set; }

    public Node(T value, IEnumerable<Node<T>> children)
    {
        this.Value = value;
        this.Children = new List<Node<T>>(children);
    }
}

这是通用的，足以用于各种问题，包括我的文本文件问题开展工作。漂亮！

**** ****更新：这里是你如何使用它：

// Given some example data:
var items = new[] 
{
   new Foo() 
   {
      Id = 1,
      ParentId = -1, // Indicates no parent
      Position = 0
   },
   new Foo() 
   {
      Id = 2,
      ParentId = 1,
      Position = 0
   },
   new Foo() 
   {
      Id = 3,
      ParentId = 1,
      Position = 1
   }
};

// Turn it into a hierarchy! 
// We'll get back a list of Node<T> containing the root nodes.
// Each node will have a list of child nodes.
var hierarchy = items.Hierarchize(
    -1, // The "root level" key. We're using -1 to indicate root level.
    f => f.Id, // The ID property on your object
    f => f.ParentId, // The property on your object that points to its parent
    f => f.Position, // The property on your object that specifies the order within its parent
    );

Answer 2

唔...我不太明白这是如何运作的。2 和 5 怎么可能都有parent=1，position=0？5 应该有父母 2、3 或 4 吗？

好的，这个新版本将所有节点遍历三次：

• 加载所有节点并将它们放入map中
• 将每个节点与其父节点关联
• 按位置对每个节点的子节点进行排序

它没有很好地封装，也没有很好的错误检查等——但它可以工作。

using System;
using System.Collections.Generic;
using System.IO;

public class Node
{
    private static readonly char[] Braces = "{}".ToCharArray();
    private static readonly char[] StringTrim = "\" ".ToCharArray();

    public Node Parent { get; set; }
    public int ParentId { get; private set; }
    public int Id { get; private set; }
    public string Title { get; private set; }
    public int Position { get; private set; }
    private readonly List<Node> children = new List<Node>();
    public List<Node> Children { get { return children; } }

    public static Node FromLine(string line)
    {
        Node node = new Node();
        line = line.Trim(Braces);
        string[] bits = line.Split(',');
        foreach (string bit in bits)
        {
            string[] keyValue = bit.Split('=');
            string key = keyValue[0].Trim();
            string value = keyValue[1].Trim();
            switch (key)
            {
                case "Id":
                    node.Id = int.Parse(value);
                    break;
                case "ParentId":
                    node.ParentId = int.Parse(value);
                    break;
                case "Position":
                    node.Position = int.Parse(value);
                    break;
                case "Title":
                    node.Title = value.Trim(StringTrim);
                    break;
                default:
                    throw new ArgumentException("Bad line: " + line);
            }
        }
        return node;
    }

    public void Dump()
    {
        int depth = 0;
        Node node = this;
        while (node.Parent != null)
        {
            depth++;
            node = node.Parent;
        }
        Console.WriteLine(new string(' ', depth * 2) + Title);
        foreach (Node child in Children)
        {
            child.Dump();
        }
    }
}

class Test
{       
    static void Main(string[] args)
    {
        var dictionary = new Dictionary<int, Node>();

        using (TextReader reader = File.OpenText("test.txt"))
        {
            string line;
            while ((line = reader.ReadLine()) != null)
            {
                Node node = Node.FromLine(line);
                dictionary[node.Id] = node;
            }
        }
        foreach (Node node in dictionary.Values)
        {
            if (node.ParentId != 0)
            {
                node.Parent = dictionary[node.ParentId];
                node.Parent.Children.Add(node);
            }
        }

        foreach (Node node in dictionary.Values)
        {
            node.Children.Sort((n1, n2) =>
                               n1.Position.CompareTo(n2.Position));
        }

        Node root = dictionary[1];
        root.Dump();
    }
}

示例文本文件：

{ Id = 5, ParentId = 4, Position = 0, Title = "grandchild 1" }
{ Id = 2, ParentId = 1, Position = 0, Title = "child 1" }
{ Id = 4, ParentId = 1, Position = 2, Title = "child 3" }
{ Id = 3, ParentId = 1, Position = 1, Title = "child 2" }
{ Id = 1, ParentId = 0, Position = 0, Title = "root" }

输出：

root
  child 1
  child 2
  child 3
    grandchild 1

Answer 3

一旦你有了你解析文件可以按照这个的博客关于如何将对象组装成使用LINQ层次。

Answer 4

我认为你的示例错误地给出了错误的父ID为对象＃5。这应该覆盖它。注意事项：假定“层次最高的”节点总是具有零父ID。忽略不最终从最上面的节点下降的任何节点。如果带有重复的ID行为将是奇数。

public class FlatObj
{
    public int Id;
    public int ParentId;
    public int Position;
    public string Title;
}

public class Node
{
    public int ID;
    public string Title;
    public IList<Node> Children;

    public Node(FlatObject baseObject, IList<Node> children)
    {
        this.ID = baseObject.Id;
        this.Title = baseObject.Title;
        this.Children = children;
    }
}

public static Node CreateHierarchy(IEnumerable<FlatObject> objects)
{
    var families = objects.ToLookup(x => x.ParentId);
    var topmost = families[0].Single();

    Func<int, IList<Node>> Children = null;

    Children = (parentID) => families[parentID]
        .OrderBy(x => x.Position)
        .Select(x => new Node(x, Children(x.Id))).ToList();

    return new Node(topmost, Children(topmost.Id));
}

public static void Test()
{
    List<FlatObj> objects = new List<FlatObj> {
    new FlatObj { Id = 1, ParentId = 0, Position = 0, Title = "root" },
    new FlatObj { Id = 2, ParentId = 1, Position = 0, Title = "child 1" },
    new FlatObj { Id = 3, ParentId = 1, Position = 1, Title = "child 2" },
    new FlatObj { Id = 4, ParentId = 1, Position = 2, Title = "child 3" },
    new FlatObj { Id = 5, ParentId = 2, Position = 0, Title = "grandchild" }};

    var nodes = CreateHierarchy(objects);
}

Answer 5

class Node {
    public int Id { get;set;  }
    public int ParentId { get;set;  }
    public int Position { get;set;  }
    public string Title { get;set;  }
    public IEnumerable<Node> Children { get; set; }

    public override string ToString() { return ToString(0); }
    public string ToString(int depth) {
        return "\n" + new string(' ', depth * 2) + Title + (
            Children.Count() == 0 ? "" :
            string.Join("", Children
                .Select(node => node.ToString(depth + 1))
                .ToArray()
            );
    }
}
class Program {
    static void Main(string[] args) {
        var data = new[] {
            new Node{ Id = 1, ParentId = 0, Position = 0, Title = "root" },
            new Node{ Id = 2, ParentId = 1, Position = 0, Title = "child 1" },
            new Node{ Id = 3, ParentId = 1, Position = 1, Title = "child 2" },
            new Node{ Id = 4, ParentId = 1, Position = 2, Title = "child 3" },
            new Node{ Id = 5, ParentId = 3, Position = 0, Title = "grandchild 1" }
        };
        Func<Node, Node> transform = null;
        transform = node => new Node {
            Title = node.Title,
            Id = node.Id,
            ParentId = node.ParentId,
            Position = node.Position,
            Children = (
                from child in data
                where child.ParentId == node.Id
                orderby child.Position
                select transform(child))
        };
        Console.WriteLine(transform(data[0]));
    }
}

结果：

root
  child 1
  child 2
    grandchild 1
  child 3

Answer 6

您一定在最后一行的PARENTID为1？标题说孙子，但它是“根”孩子，如果我正确地阅读的东西。

Answer 7

下面是@baran要求的示例：

var lHierarchicalMenuItems = lMenuItemsFromDB.Hierarchize(0, aItem => aItem.Id, aItem => aItem.ParentId, aItem => aItem.Position);