將對象屬性值轉換為字典

Question

可以說，我有一個像這樣的對象列表

public class Room{
    public string Name {get; set;}
    public int[] UserId {get; set;}
}

什么是將此列表轉換為字典的有效方式，如下所示

Dictionary<int, List<string>> 

其中鍵是UserId，String是房間的名稱。 提前致謝。

Answer 1

我會使用Linq的Aggregate方法，如下所示。 （ 注意我將原始對象的自由作為一個List vs一個數組用於演示，但你可以改變它 ）。

var names = new List<Room>()
{
    new Room() { Name = "Alpha", UserId = new List<int> { 10, 40 }},
    new Room() { Name = "Omega", UserId = new List<int> { 10, 20, 30 }},
};

// Aggregate needs an item to pass around, we will
// seed it with the dictionary which will be the ultimate returned
// value. The following lambda takes a dictionary object (`dict`)
// and the current room ('current') to add to the dictionary. 
names.Aggregate (new Dictionary<int, List<string>>(), (dict, current) =>
            {
               current.UserId.ForEach(id => {
                                               if (dict.ContainsKey(id) == false)
                                                  dict.Add(id, new List<string>());

                                               dict[id].Add(current.Name);
                                            });
                return dict;
            });

結果：

Answer 2

概念

• 遍歷房間列表。
• 如果字典包含UserID，則將名稱添加到關聯列表。
• 否則制作一個新的字典項目。

履行

foreach (Room r in RoomsList) {
    foreach (int id in r.UserID) {
        if (RoomDictionary.Contains(id))
            RoomDictionary[id].Add(r.Name);
        else
            RoomDicationary.Add(id, new List<string>() { r.Name });
    }
}

或者類似的東西，我只是在網絡瀏覽器中鍵入它，所以它可能需要一些調整，但類似的東西。

Answer 3

只是一些澄清，因為UserId被聲明為類Room中的數組。 假設它不是數組，1個id對應1個房間名稱。 實現IDictionary的RoomCollection將為您提供更好的控制，如下所示：

 public class RoomCollection : IDictionary<int, string>
{
    private Dictionary<int, string> roomCollection = new Dictionary<int, string>();

    //Add modified version of Add()
    public void Add(Room room)
    {
        //Do something to efficiently check whether room already exists
        this.Add(room.UserId, room.Name);
    }

    public void Add(int key, string value)
    {
        //Checking can be done here
        if (this.roomCollection.ContainsKey(key))
        {
            this.roomCollection[key] = value; //Overwrite values
        }
        else
        {
            this.roomCollection.Add(key, value); //Create new item
        }
    }

    //Modify other functionalities to your own liking
    public bool ContainsKey(int key)
    {
        return this.roomCollection.ContainsKey(key);
    }

    public ICollection<int> Keys
    {
        get { throw new NotImplementedException(); }
    }

    public bool Remove(int key)
    {
        throw new NotImplementedException();
    }

    public bool TryGetValue(int key, out string value)
    {
        throw new NotImplementedException();
    }

    public ICollection<string> Values
    {
        get { throw new NotImplementedException(); }
    }

    public string this[int key]
    {
        get
        {
            throw new NotImplementedException();
        }
        set
        {
            throw new NotImplementedException();
        }
    }

    public void Add(KeyValuePair<int, string> item)
    {
        throw new NotImplementedException();
    }

    public void Clear()
    {
        throw new NotImplementedException();
    }

    public bool Contains(KeyValuePair<int, string> item)
    {
        throw new NotImplementedException();
    }

    public void CopyTo(KeyValuePair<int, string>[] array, int arrayIndex)
    {
        throw new NotImplementedException();
    }

    public int Count
    {
        get { throw new NotImplementedException(); }
    }

    public bool IsReadOnly
    {
        get { throw new NotImplementedException(); }
    }

    public bool Remove(KeyValuePair<int, string> item)
    {
        throw new NotImplementedException();
    }

    public IEnumerator<KeyValuePair<int, string>> GetEnumerator()
    {
        throw new NotImplementedException();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        throw new NotImplementedException();
    }
}

public class Room
{
    public string Name { get; set; }
    public int UserId { get; set; }
}

public class TestCollection
{
    public void Test()
    {
        Room r1 = new Room();
        r1.UserId = 1;
        r1.Name = "Room One";

        Room r2 = new Room();
        r2.UserId = 2;
        r2.Name = "Room Two";

        RoomCollection roomCollection = new RoomCollection();
        roomCollection.Add(r1);
        roomCollection.Add(r2);

        foreach (int roomId in roomCollection.Keys)
        {
            Console.WriteLine("Room number: {0} - Room name: {1}", roomId, roomCollection[roomId]);
        }
    }
}

Answer 4

這似乎很直接：

var rooms = new List<Room>()
{
    new Room() { Name = "Alpha", UserId = new List<int>() { 10, 40 }.ToArray() },
    new Room() { Name = "Omega", UserId = new List<int>() { 10, 20, 30 }.ToArray() },
};

var query =
    from r in rooms
    from u in r.UserId 
    group r.Name by u;

var result = query.ToDictionary(x => x.Key, x => x.ToList());

我得到的結果是：