Diccionario bidireccional 1 a 1 en C #

Estoy buscando una clase de diccionario 1 a 1 bidireccional genérica en C # (2), es decir. a BiDictionaryOneToOne<T, S>que está garantizado para contener solo uno de cada valor y clave (hasta RefEquals de todos modos), y que se puede buscar utilizando la clave o el valor. ¿Alguien sabe de uno, o debería implementarlo yo mismo? No puedo creer que sea la primera persona en necesitar esto ...

Hay un BiDictionary en las respuestas a esta pregunta , pero no es para elementos únicos (y tampoco implementa RemoveByFirst (T t) o RemoveBySecond (S s)).

¡Gracias!

OK, aquí está mi intento (basado en el de Jon, gracias), archivado aquí y abierto para mejoras:

/// <summary>
/// This is a dictionary guaranteed to have only one of each value and key. 
/// It may be searched either by TFirst or by TSecond, giving a unique answer because it is 1 to 1.
/// </summary>
/// <typeparam name="TFirst">The type of the "key"</typeparam>
/// <typeparam name="TSecond">The type of the "value"</typeparam>
public class BiDictionaryOneToOne<TFirst, TSecond>
{
    IDictionary<TFirst, TSecond> firstToSecond = new Dictionary<TFirst, TSecond>();
    IDictionary<TSecond, TFirst> secondToFirst = new Dictionary<TSecond, TFirst>();

    #region Exception throwing methods

    /// <summary>
    /// Tries to add the pair to the dictionary.
    /// Throws an exception if either element is already in the dictionary
    /// </summary>
    /// <param name="first"></param>
    /// <param name="second"></param>
    public void Add(TFirst first, TSecond second)
    {
        if (firstToSecond.ContainsKey(first) || secondToFirst.ContainsKey(second))
            throw new ArgumentException("Duplicate first or second");

        firstToSecond.Add(first, second);
        secondToFirst.Add(second, first);
    }

    /// <summary>
    /// Find the TSecond corresponding to the TFirst first
    /// Throws an exception if first is not in the dictionary.
    /// </summary>
    /// <param name="first">the key to search for</param>
    /// <returns>the value corresponding to first</returns>
    public TSecond GetByFirst(TFirst first)
    {
        TSecond second;
        if (!firstToSecond.TryGetValue(first, out second))
            throw new ArgumentException("first");

        return second; 
    }

    /// <summary>
    /// Find the TFirst corresponing to the Second second.
    /// Throws an exception if second is not in the dictionary.
    /// </summary>
    /// <param name="second">the key to search for</param>
    /// <returns>the value corresponding to second</returns>
    public TFirst GetBySecond(TSecond second)
    {
        TFirst first;
        if (!secondToFirst.TryGetValue(second, out first))
            throw new ArgumentException("second");

        return first; 
    }


    /// <summary>
    /// Remove the record containing first.
    /// If first is not in the dictionary, throws an Exception.
    /// </summary>
    /// <param name="first">the key of the record to delete</param>
    public void RemoveByFirst(TFirst first)
    {
        TSecond second;
        if (!firstToSecond.TryGetValue(first, out second))
            throw new ArgumentException("first");

        firstToSecond.Remove(first);
        secondToFirst.Remove(second);
    }

    /// <summary>
    /// Remove the record containing second.
    /// If second is not in the dictionary, throws an Exception.
    /// </summary>
    /// <param name="second">the key of the record to delete</param>
    public void RemoveBySecond(TSecond second)
    {
        TFirst first;
        if (!secondToFirst.TryGetValue(second, out first))
            throw new ArgumentException("second");

        secondToFirst.Remove(second);
        firstToSecond.Remove(first);
    }

    #endregion

    #region Try methods

    /// <summary>
    /// Tries to add the pair to the dictionary.
    /// Returns false if either element is already in the dictionary        
    /// </summary>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <returns>true if successfully added, false if either element are already in the dictionary</returns>
    public Boolean TryAdd(TFirst first, TSecond second)
    {
        if (firstToSecond.ContainsKey(first) || secondToFirst.ContainsKey(second))
            return false;

        firstToSecond.Add(first, second);
        secondToFirst.Add(second, first);
        return true;
    }


    /// <summary>
    /// Find the TSecond corresponding to the TFirst first.
    /// Returns false if first is not in the dictionary.
    /// </summary>
    /// <param name="first">the key to search for</param>
    /// <param name="second">the corresponding value</param>
    /// <returns>true if first is in the dictionary, false otherwise</returns>
    public Boolean TryGetByFirst(TFirst first, out TSecond second)
    {
        return firstToSecond.TryGetValue(first, out second);
    }

    /// <summary>
    /// Find the TFirst corresponding to the TSecond second.
    /// Returns false if second is not in the dictionary.
    /// </summary>
    /// <param name="second">the key to search for</param>
    /// <param name="first">the corresponding value</param>
    /// <returns>true if second is in the dictionary, false otherwise</returns>
    public Boolean TryGetBySecond(TSecond second, out TFirst first)
    {
        return secondToFirst.TryGetValue(second, out first);
    }

    /// <summary>
    /// Remove the record containing first, if there is one.
    /// </summary>
    /// <param name="first"></param>
    /// <returns> If first is not in the dictionary, returns false, otherwise true</returns>
    public Boolean TryRemoveByFirst(TFirst first)
    {
        TSecond second;
        if (!firstToSecond.TryGetValue(first, out second))
            return false;

        firstToSecond.Remove(first);
        secondToFirst.Remove(second);
        return true;
    }

    /// <summary>
    /// Remove the record containing second, if there is one.
    /// </summary>
    /// <param name="second"></param>
    /// <returns> If second is not in the dictionary, returns false, otherwise true</returns>
    public Boolean TryRemoveBySecond(TSecond second)
    {
        TFirst first;
        if (!secondToFirst.TryGetValue(second, out first))
            return false;

        secondToFirst.Remove(second);
        firstToSecond.Remove(first);
        return true;
    }

    #endregion        

    /// <summary>
    /// The number of pairs stored in the dictionary
    /// </summary>
    public Int32 Count
    {
        get { return firstToSecond.Count; }
    }

    /// <summary>
    /// Removes all items from the dictionary.
    /// </summary>
    public void Clear()
    {
        firstToSecond.Clear();
        secondToFirst.Clear();
    }
}

Una implementación más completa del diccionario bidireccional:

• Admite casi todas las interfaces originales Dictionary<TKey,TValue>(excepto las interfaces de infraestructura):
  • IDictionary<TKey, TValue>
  • IReadOnlyDictionary<TKey, TValue>
  • IDictionary
  • ICollection<KeyValuePair<TKey, TValue>> (esta y las siguientes son las interfaces base de las anteriores)
  • ICollection
  • IReadOnlyCollection<KeyValuePair<TKey, TValue>>
  • IEnumerable<KeyValuePair<TKey, TValue>>
  • IEnumerable
• Serialización usando SerializableAttribute.
• Vista de depuración usando DebuggerDisplayAttribute(con información de recuento) y DebuggerTypeProxyAttribute(para mostrar pares clave-valor en relojes).
• El diccionario inverso está disponible como IDictionary<TValue, TKey> Reversepropiedad y también implementa todas las interfaces mencionadas anteriormente. Todas las operaciones en cualquiera de los diccionarios modifican ambos.

Uso:

var dic = new BiDictionary<int, string>();
dic.Add(1, "1");
dic[2] = "2";
dic.Reverse.Add("3", 3);
dic.Reverse["4"] = 4;
dic.Clear();

El código está disponible en mi marco privado en GitHub: BiDictionary (TFirst, TSecond) .cs ( enlace permanente , búsqueda ).

Copiar:

[Serializable]
[DebuggerDisplay ("Count = {Count}"), DebuggerTypeProxy (typeof(DictionaryDebugView<,>))]
public class BiDictionary<TFirst, TSecond> : IDictionary<TFirst, TSecond>, IReadOnlyDictionary<TFirst, TSecond>, IDictionary
{
    private readonly IDictionary<TFirst, TSecond> _firstToSecond = new Dictionary<TFirst, TSecond>();
    [NonSerialized]
    private readonly IDictionary<TSecond, TFirst> _secondToFirst = new Dictionary<TSecond, TFirst>();
    [NonSerialized]
    private readonly ReverseDictionary _reverseDictionary;

    public BiDictionary ()
    {
        _reverseDictionary = new ReverseDictionary(this);
    }

    public IDictionary<TSecond, TFirst> Reverse
    {
        get { return _reverseDictionary; }
    }

    public int Count
    {
        get { return _firstToSecond.Count; }
    }

    object ICollection.SyncRoot
    {
        get { return ((ICollection)_firstToSecond).SyncRoot; }
    }

    bool ICollection.IsSynchronized
    {
        get { return ((ICollection)_firstToSecond).IsSynchronized; }
    }

    bool IDictionary.IsFixedSize
    {
        get { return ((IDictionary)_firstToSecond).IsFixedSize; }
    }

    public bool IsReadOnly
    {
        get { return _firstToSecond.IsReadOnly || _secondToFirst.IsReadOnly; }
    }

    public TSecond this [TFirst key]
    {
        get { return _firstToSecond[key]; }
        set
        {
            _firstToSecond[key] = value;
            _secondToFirst[value] = key;
        }
    }

    object IDictionary.this [object key]
    {
        get { return ((IDictionary)_firstToSecond)[key]; }
        set
        {
            ((IDictionary)_firstToSecond)[key] = value;
            ((IDictionary)_secondToFirst)[value] = key;
        }
    }

    public ICollection<TFirst> Keys
    {
        get { return _firstToSecond.Keys; }
    }

    ICollection IDictionary.Keys
    {
        get { return ((IDictionary)_firstToSecond).Keys; }
    }

    IEnumerable<TFirst> IReadOnlyDictionary<TFirst, TSecond>.Keys
    {
        get { return ((IReadOnlyDictionary<TFirst, TSecond>)_firstToSecond).Keys; }
    }

    public ICollection<TSecond> Values
    {
        get { return _firstToSecond.Values; }
    }

    ICollection IDictionary.Values
    {
        get { return ((IDictionary)_firstToSecond).Values; }
    }

    IEnumerable<TSecond> IReadOnlyDictionary<TFirst, TSecond>.Values
    {
        get { return ((IReadOnlyDictionary<TFirst, TSecond>)_firstToSecond).Values; }
    }

    public IEnumerator<KeyValuePair<TFirst, TSecond>> GetEnumerator ()
    {
        return _firstToSecond.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator ()
    {
        return GetEnumerator();
    }

    IDictionaryEnumerator IDictionary.GetEnumerator ()
    {
        return ((IDictionary)_firstToSecond).GetEnumerator();
    }

    public void Add (TFirst key, TSecond value)
    {
        _firstToSecond.Add(key, value);
        _secondToFirst.Add(value, key);
    }

    void IDictionary.Add (object key, object value)
    {
        ((IDictionary)_firstToSecond).Add(key, value);
        ((IDictionary)_secondToFirst).Add(value, key);
    }

    public void Add (KeyValuePair<TFirst, TSecond> item)
    {
        _firstToSecond.Add(item);
        _secondToFirst.Add(item.Reverse());
    }

    public bool ContainsKey (TFirst key)
    {
        return _firstToSecond.ContainsKey(key);
    }

    public bool Contains (KeyValuePair<TFirst, TSecond> item)
    {
        return _firstToSecond.Contains(item);
    }

    public bool TryGetValue (TFirst key, out TSecond value)
    {
        return _firstToSecond.TryGetValue(key, out value);
    }

    public bool Remove (TFirst key)
    {
        TSecond value;
        if (_firstToSecond.TryGetValue(key, out value)) {
            _firstToSecond.Remove(key);
            _secondToFirst.Remove(value);
            return true;
        }
        else
            return false;
    }

    void IDictionary.Remove (object key)
    {
        var firstToSecond = (IDictionary)_firstToSecond;
        if (!firstToSecond.Contains(key))
            return;
        var value = firstToSecond[key];
        firstToSecond.Remove(key);
        ((IDictionary)_secondToFirst).Remove(value);
    }

    public bool Remove (KeyValuePair<TFirst, TSecond> item)
    {
        return _firstToSecond.Remove(item);
    }

    public bool Contains (object key)
    {
        return ((IDictionary)_firstToSecond).Contains(key);
    }

    public void Clear ()
    {
        _firstToSecond.Clear();
        _secondToFirst.Clear();
    }

    public void CopyTo (KeyValuePair<TFirst, TSecond>[] array, int arrayIndex)
    {
        _firstToSecond.CopyTo(array, arrayIndex);
    }

    void ICollection.CopyTo (Array array, int index)
    {
        ((IDictionary)_firstToSecond).CopyTo(array, index);
    }

    [OnDeserialized]
    internal void OnDeserialized (StreamingContext context)
    {
        _secondToFirst.Clear();
        foreach (var item in _firstToSecond)
            _secondToFirst.Add(item.Value, item.Key);
    }

    private class ReverseDictionary : IDictionary<TSecond, TFirst>, IReadOnlyDictionary<TSecond, TFirst>, IDictionary
    {
        private readonly BiDictionary<TFirst, TSecond> _owner;

        public ReverseDictionary (BiDictionary<TFirst, TSecond> owner)
        {
            _owner = owner;
        }

        public int Count
        {
            get { return _owner._secondToFirst.Count; }
        }

        object ICollection.SyncRoot
        {
            get { return ((ICollection)_owner._secondToFirst).SyncRoot; }
        }

        bool ICollection.IsSynchronized
        {
            get { return ((ICollection)_owner._secondToFirst).IsSynchronized; }
        }

        bool IDictionary.IsFixedSize
        {
            get { return ((IDictionary)_owner._secondToFirst).IsFixedSize; }
        }

        public bool IsReadOnly
        {
            get { return _owner._secondToFirst.IsReadOnly || _owner._firstToSecond.IsReadOnly; }
        }

        public TFirst this [TSecond key]
        {
            get { return _owner._secondToFirst[key]; }
            set
            {
                _owner._secondToFirst[key] = value;
                _owner._firstToSecond[value] = key;
            }
        }

        object IDictionary.this [object key]
        {
            get { return ((IDictionary)_owner._secondToFirst)[key]; }
            set
            {
                ((IDictionary)_owner._secondToFirst)[key] = value;
                ((IDictionary)_owner._firstToSecond)[value] = key;
            }
        }

        public ICollection<TSecond> Keys
        {
            get { return _owner._secondToFirst.Keys; }
        }

        ICollection IDictionary.Keys
        {
            get { return ((IDictionary)_owner._secondToFirst).Keys; }
        }

        IEnumerable<TSecond> IReadOnlyDictionary<TSecond, TFirst>.Keys
        {
            get { return ((IReadOnlyDictionary<TSecond, TFirst>)_owner._secondToFirst).Keys; }
        }

        public ICollection<TFirst> Values
        {
            get { return _owner._secondToFirst.Values; }
        }

        ICollection IDictionary.Values
        {
            get { return ((IDictionary)_owner._secondToFirst).Values; }
        }

        IEnumerable<TFirst> IReadOnlyDictionary<TSecond, TFirst>.Values
        {
            get { return ((IReadOnlyDictionary<TSecond, TFirst>)_owner._secondToFirst).Values; }
        }

        public IEnumerator<KeyValuePair<TSecond, TFirst>> GetEnumerator ()
        {
            return _owner._secondToFirst.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator ()
        {
            return GetEnumerator();
        }

        IDictionaryEnumerator IDictionary.GetEnumerator ()
        {
            return ((IDictionary)_owner._secondToFirst).GetEnumerator();
        }

        public void Add (TSecond key, TFirst value)
        {
            _owner._secondToFirst.Add(key, value);
            _owner._firstToSecond.Add(value, key);
        }

        void IDictionary.Add (object key, object value)
        {
            ((IDictionary)_owner._secondToFirst).Add(key, value);
            ((IDictionary)_owner._firstToSecond).Add(value, key);
        }

        public void Add (KeyValuePair<TSecond, TFirst> item)
        {
            _owner._secondToFirst.Add(item);
            _owner._firstToSecond.Add(item.Reverse());
        }

        public bool ContainsKey (TSecond key)
        {
            return _owner._secondToFirst.ContainsKey(key);
        }

        public bool Contains (KeyValuePair<TSecond, TFirst> item)
        {
            return _owner._secondToFirst.Contains(item);
        }

        public bool TryGetValue (TSecond key, out TFirst value)
        {
            return _owner._secondToFirst.TryGetValue(key, out value);
        }

        public bool Remove (TSecond key)
        {
            TFirst value;
            if (_owner._secondToFirst.TryGetValue(key, out value)) {
                _owner._secondToFirst.Remove(key);
                _owner._firstToSecond.Remove(value);
                return true;
            }
            else
                return false;
        }

        void IDictionary.Remove (object key)
        {
            var firstToSecond = (IDictionary)_owner._secondToFirst;
            if (!firstToSecond.Contains(key))
                return;
            var value = firstToSecond[key];
            firstToSecond.Remove(key);
            ((IDictionary)_owner._firstToSecond).Remove(value);
        }

        public bool Remove (KeyValuePair<TSecond, TFirst> item)
        {
            return _owner._secondToFirst.Remove(item);
        }

        public bool Contains (object key)
        {
            return ((IDictionary)_owner._secondToFirst).Contains(key);
        }

        public void Clear ()
        {
            _owner._secondToFirst.Clear();
            _owner._firstToSecond.Clear();
        }

        public void CopyTo (KeyValuePair<TSecond, TFirst>[] array, int arrayIndex)
        {
            _owner._secondToFirst.CopyTo(array, arrayIndex);
        }

        void ICollection.CopyTo (Array array, int index)
        {
            ((IDictionary)_owner._secondToFirst).CopyTo(array, index);
        }
    }
}

internal class DictionaryDebugView<TKey, TValue>
{
    private readonly IDictionary<TKey, TValue> _dictionary;

    [DebuggerBrowsable (DebuggerBrowsableState.RootHidden)]
    public KeyValuePair<TKey, TValue>[] Items
    {
        get
        {
            var array = new KeyValuePair<TKey, TValue>[_dictionary.Count];
            _dictionary.CopyTo(array, 0);
            return array;
        }
    }

    public DictionaryDebugView (IDictionary<TKey, TValue> dictionary)
    {
        if (dictionary == null)
            throw new ArgumentNullException("dictionary");
        _dictionary = dictionary;
    }
}

public static class KeyValuePairExts
{
    public static KeyValuePair<TValue, TKey> Reverse<TKey, TValue> (this KeyValuePair<TKey, TValue> @this)
    {
        return new KeyValuePair<TValue, TKey>(@this.Value, @this.Key);
    }
}

La pregunta a la que hace referencia también muestra una implementación uno a uno en esta respuesta . Agregar RemoveByFirst y RemoveBySecond sería trivial, al igual que implementar interfaces adicionales, etc.

Esta es la misma que la respuesta aceptada, pero también proporcioné Updatemétodos y, sobre todo, un poco más desarrollado:

public class BiDictionary<TKey1, TKey2> : IEnumerable<Tuple<TKey1, TKey2>>
{
    Dictionary<TKey1, TKey2> _forwards;
    Dictionary<TKey2, TKey1> _reverses;

    public int Count
    {
        get
        {
            if (_forwards.Count != _reverses.Count)
                throw new Exception("somewhere logic went wrong and your data got corrupt");

            return _forwards.Count;
        }
    }

    public ICollection<TKey1> Key1s
    {
        get { return _forwards.Keys; }
    }

    public ICollection<TKey2> Key2s
    {
        get { return _reverses.Keys; }
    }

    public BiDictionary(IEqualityComparer<TKey1> comparer1 = null, IEqualityComparer<TKey2> comparer2 = null)
    {
        _forwards = new Dictionary<TKey1, TKey2>(comparer1);
        _reverses = new Dictionary<TKey2, TKey1>(comparer2);
    }



    public bool ContainsKey1(TKey1 key)
    {
        return ContainsKey(key, _forwards);
    }

    private static bool ContainsKey<S, T>(S key, Dictionary<S, T> dict)
    {
        return dict.ContainsKey(key);
    }

    public bool ContainsKey2(TKey2 key)
    {
        return ContainsKey(key, _reverses);
    }

    public TKey2 GetValueByKey1(TKey1 key)
    {
        return GetValueByKey(key, _forwards);
    }

    private static T GetValueByKey<S, T>(S key, Dictionary<S, T> dict)
    {
        return dict[key];
    }

    public TKey1 GetValueByKey2(TKey2 key)
    {
        return GetValueByKey(key, _reverses);
    }

    public bool TryGetValueByKey1(TKey1 key, out TKey2 value)
    {
        return TryGetValue(key, _forwards, out value);
    }

    private static bool TryGetValue<S, T>(S key, Dictionary<S, T> dict, out T value)
    {
        return dict.TryGetValue(key, out value);
    }

    public bool TryGetValueByKey2(TKey2 key, out TKey1 value)
    {
        return TryGetValue(key, _reverses, out value);
    }

    public bool Add(TKey1 key1, TKey2 key2)
    {
        if (ContainsKey1(key1) || ContainsKey2(key2))   // very important
            return false;

        AddOrUpdate(key1, key2);
        return true;
    }

    public void AddOrUpdateByKey1(TKey1 key1, TKey2 key2)
    {
        if (!UpdateByKey1(key1, key2))
            AddOrUpdate(key1, key2);
    }

    // dont make this public; a dangerous method used cautiously in this class
    private void AddOrUpdate(TKey1 key1, TKey2 key2)
    {
        _forwards[key1] = key2;
        _reverses[key2] = key1;
    }

    public void AddOrUpdateKeyByKey2(TKey2 key2, TKey1 key1)
    {
        if (!UpdateByKey2(key2, key1))
            AddOrUpdate(key1, key2);
    }

    public bool UpdateKey1(TKey1 oldKey, TKey1 newKey)
    {
        return UpdateKey(oldKey, _forwards, newKey, (key1, key2) => AddOrUpdate(key1, key2));
    }

    private static bool UpdateKey<S, T>(S oldKey, Dictionary<S, T> dict, S newKey, Action<S, T> updater)
    {
        T otherKey;
        if (!TryGetValue(oldKey, dict, out otherKey) || ContainsKey(newKey, dict))
            return false;

        Remove(oldKey, dict);
        updater(newKey, otherKey);
        return true;
    }

    public bool UpdateKey2(TKey2 oldKey, TKey2 newKey)
    {
        return UpdateKey(oldKey, _reverses, newKey, (key1, key2) => AddOrUpdate(key2, key1));
    }

    public bool UpdateByKey1(TKey1 key1, TKey2 key2)
    {
        return UpdateByKey(key1, _forwards, _reverses, key2, (k1, k2) => AddOrUpdate(k1, k2));
    }

    private static bool UpdateByKey<S, T>(S key1, Dictionary<S, T> forwards, Dictionary<T, S> reverses, T key2,
                                          Action<S, T> updater)
    {
        T otherKey;
        if (!TryGetValue(key1, forwards, out otherKey) || ContainsKey(key2, reverses))
            return false;

        if (!Remove(otherKey, reverses))
            throw new Exception("somewhere logic went wrong and your data got corrupt");

        updater(key1, key2);
        return true;
    }

    public bool UpdateByKey2(TKey2 key2, TKey1 key1)
    {
        return UpdateByKey(key2, _reverses, _forwards, key1, (k1, k2) => AddOrUpdate(k2, k1));
    }

    public bool RemoveByKey1(TKey1 key)
    {
        return RemoveByKey(key, _forwards, _reverses);
    }

    private static bool RemoveByKey<S, T>(S key, Dictionary<S, T> keyDict, Dictionary<T, S> valueDict)
    {
        T otherKey;
        if (!TryGetValue(key, keyDict, out otherKey))
            return false;

        if (!Remove(key, keyDict) || !Remove(otherKey, valueDict))
            throw new Exception("somewhere logic went wrong and your data got corrupt");

        return true;
    }

    private static bool Remove<S, T>(S key, Dictionary<S, T> dict)
    {
        return dict.Remove(key);
    }

    public bool RemoveByKey2(TKey2 key)
    {
        return RemoveByKey(key, _reverses, _forwards);
    }

    public void Clear()
    {
        _forwards.Clear();
        _reverses.Clear();
    }

    public IEnumerator<Tuple<TKey1, TKey2>> GetEnumerator()
    {
        if (_forwards.Count != _reverses.Count)
            throw new Exception("somewhere logic went wrong and your data got corrupt");

        foreach (var item in _forwards)
            yield return Tuple.Create(item.Key, item.Value);
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

Similar a mi respuesta aquí

Algunas cosas a tener en cuenta:

1. Solo he implementado IEnumerable<>. No creo que ICollection<>tenga sentido aquí, ya que los nombres de los métodos podrían ser muy diferentes para esta estructura de colección especial. Depende de usted decidir qué debe ir dentro IEnumerable<>. Así que ahora también tiene la sintaxis del inicializador de colección, como

   var p = new BiDictionary<int, string> { 1, "a" }, { 2, "b" } };

2. He intentado lanzar algunas excepciones extrañas aquí y allá, solo para la integridad de los datos. Solo para estar más seguro y saber si alguna vez mi código tiene errores.

3. Rendimiento: puede buscar Valuecon cualquiera de los Keysmedios Gety Containsmétodos que requieren solo 1 búsqueda (O (1)). Addrequiere 2 búsquedas y 2 adiciones. Updaterequiere 1 búsqueda y 2 adiciones. Removetoma 3 búsquedas. Todo similar a la respuesta aceptada.

He creado una clase de este tipo, utilizando clases de colección C5.

public class Mapper<K,T> : IEnumerable<T>

{
    C5.TreeDictionary<K,T> KToTMap = new TreeDictionary<K,T>();
    C5.HashDictionary<T,K> TToKMap = new HashDictionary<T,K>();


    /// <summary>
    /// Initializes a new instance of the Mapper class.
    /// </summary>
    public Mapper()
    {
        KToTMap = new TreeDictionary<K,T>();
        TToKMap = new HashDictionary<T,K>();
    }


    public void Add(K key, T value)
    {
        KToTMap.Add(key, value);
        TToKMap.Add(value, key);
    }

    public bool ContainsKey(K key)
    {
        return KToTMap.Contains(key);
    }

    public int Count
    {
        get { return KToTMap.Count; }
    }


    public K this[T obj]
    {
        get
        {
            return TToKMap[obj];
        }
    }

    public T this[K obj]
    {
        get
        {
            return KToTMap[obj];
        }
    }

    public IEnumerator<T> GetEnumerator()
    {
        return KToTMap.Values.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return KToTMap.Values.GetEnumerator();
    }
}

Otra extensión de la respuesta aceptada. Implementa IEnumerable para que uno pueda usar foreach con eso. Me doy cuenta de que hay más respuestas con la implementación de IEnumerable, pero esta usa estructuras, por lo que es compatible con el recolector de basura . Esto es especialmente útil en el motor Unity (verificado con el generador de perfiles).

/// <summary>
/// This is a dictionary guaranteed to have only one of each value and key. 
/// It may be searched either by TFirst or by TSecond, giving a unique answer because it is 1 to 1.
/// It implements garbage-collector-friendly IEnumerable.
/// </summary>
/// <typeparam name="TFirst">The type of the "key"</typeparam>
/// <typeparam name="TSecond">The type of the "value"</typeparam>
public class BiDictionary<TFirst, TSecond> : IEnumerable<BiDictionary<TFirst, TSecond>.Pair>
{


    public struct Pair
    {
        public TFirst  First;
        public TSecond Second;
    }


    public struct Enumerator : IEnumerator<Pair>, IEnumerator
    {

        public Enumerator(Dictionary<TFirst, TSecond>.Enumerator dictEnumerator)
        {
            _dictEnumerator = dictEnumerator;
        }

        public Pair Current
        {
            get
            {
                Pair pair;
                pair.First = _dictEnumerator.Current.Key;
                pair.Second = _dictEnumerator.Current.Value;
                return pair;
            }
        }

        object IEnumerator.Current
        {
            get
            {
                return Current;
            }
        }

        public void Dispose()
        {
            _dictEnumerator.Dispose();
        }

        public bool MoveNext()
        {
            return _dictEnumerator.MoveNext();
        }

        public void Reset()
        {
            throw new NotSupportedException();
        }

        private Dictionary<TFirst, TSecond>.Enumerator _dictEnumerator;

    }

    #region Exception throwing methods

    /// <summary>
    /// Tries to add the pair to the dictionary.
    /// Throws an exception if either element is already in the dictionary
    /// </summary>
    /// <param name="first"></param>
    /// <param name="second"></param>
    public void Add(TFirst first, TSecond second)
    {
        if (_firstToSecond.ContainsKey(first) || _secondToFirst.ContainsKey(second))
            throw new ArgumentException("Duplicate first or second");

        _firstToSecond.Add(first, second);
        _secondToFirst.Add(second, first);
    }

    /// <summary>
    /// Find the TSecond corresponding to the TFirst first
    /// Throws an exception if first is not in the dictionary.
    /// </summary>
    /// <param name="first">the key to search for</param>
    /// <returns>the value corresponding to first</returns>
    public TSecond GetByFirst(TFirst first)
    {
        TSecond second;
        if (!_firstToSecond.TryGetValue(first, out second))
            throw new ArgumentException("first");

        return second;
    }

    /// <summary>
    /// Find the TFirst corresponing to the Second second.
    /// Throws an exception if second is not in the dictionary.
    /// </summary>
    /// <param name="second">the key to search for</param>
    /// <returns>the value corresponding to second</returns>
    public TFirst GetBySecond(TSecond second)
    {
        TFirst first;
        if (!_secondToFirst.TryGetValue(second, out first))
            throw new ArgumentException("second");

        return first;
    }


    /// <summary>
    /// Remove the record containing first.
    /// If first is not in the dictionary, throws an Exception.
    /// </summary>
    /// <param name="first">the key of the record to delete</param>
    public void RemoveByFirst(TFirst first)
    {
        TSecond second;
        if (!_firstToSecond.TryGetValue(first, out second))
            throw new ArgumentException("first");

        _firstToSecond.Remove(first);
        _secondToFirst.Remove(second);
    }

    /// <summary>
    /// Remove the record containing second.
    /// If second is not in the dictionary, throws an Exception.
    /// </summary>
    /// <param name="second">the key of the record to delete</param>
    public void RemoveBySecond(TSecond second)
    {
        TFirst first;
        if (!_secondToFirst.TryGetValue(second, out first))
            throw new ArgumentException("second");

        _secondToFirst.Remove(second);
        _firstToSecond.Remove(first);
    }

    #endregion

    #region Try methods

    /// <summary>
    /// Tries to add the pair to the dictionary.
    /// Returns false if either element is already in the dictionary        
    /// </summary>
    /// <param name="first"></param>
    /// <param name="second"></param>
    /// <returns>true if successfully added, false if either element are already in the dictionary</returns>
    public bool TryAdd(TFirst first, TSecond second)
    {
        if (_firstToSecond.ContainsKey(first) || _secondToFirst.ContainsKey(second))
            return false;

        _firstToSecond.Add(first, second);
        _secondToFirst.Add(second, first);
        return true;
    }


    /// <summary>
    /// Find the TSecond corresponding to the TFirst first.
    /// Returns false if first is not in the dictionary.
    /// </summary>
    /// <param name="first">the key to search for</param>
    /// <param name="second">the corresponding value</param>
    /// <returns>true if first is in the dictionary, false otherwise</returns>
    public bool TryGetByFirst(TFirst first, out TSecond second)
    {
        return _firstToSecond.TryGetValue(first, out second);
    }

    /// <summary>
    /// Find the TFirst corresponding to the TSecond second.
    /// Returns false if second is not in the dictionary.
    /// </summary>
    /// <param name="second">the key to search for</param>
    /// <param name="first">the corresponding value</param>
    /// <returns>true if second is in the dictionary, false otherwise</returns>
    public bool TryGetBySecond(TSecond second, out TFirst first)
    {
        return _secondToFirst.TryGetValue(second, out first);
    }

    /// <summary>
    /// Remove the record containing first, if there is one.
    /// </summary>
    /// <param name="first"></param>
    /// <returns> If first is not in the dictionary, returns false, otherwise true</returns>
    public bool TryRemoveByFirst(TFirst first)
    {
        TSecond second;
        if (!_firstToSecond.TryGetValue(first, out second))
            return false;

        _firstToSecond.Remove(first);
        _secondToFirst.Remove(second);
        return true;
    }

    /// <summary>
    /// Remove the record containing second, if there is one.
    /// </summary>
    /// <param name="second"></param>
    /// <returns> If second is not in the dictionary, returns false, otherwise true</returns>
    public bool TryRemoveBySecond(TSecond second)
    {
        TFirst first;
        if (!_secondToFirst.TryGetValue(second, out first))
            return false;

        _secondToFirst.Remove(second);
        _firstToSecond.Remove(first);
        return true;
    }

    #endregion        

    /// <summary>
    /// The number of pairs stored in the dictionary
    /// </summary>
    public Int32 Count
    {
        get { return _firstToSecond.Count; }
    }

    /// <summary>
    /// Removes all items from the dictionary.
    /// </summary>
    public void Clear()
    {
        _firstToSecond.Clear();
        _secondToFirst.Clear();
    }


    public Enumerator GetEnumerator()
    {
        //enumerator.Reset(firstToSecond.GetEnumerator());
        return new Enumerator(_firstToSecond.GetEnumerator());
    }

    IEnumerator<Pair> IEnumerable<Pair>.GetEnumerator()
    {
        return GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }



    private Dictionary<TFirst, TSecond> _firstToSecond  = new Dictionary<TFirst, TSecond>();
    private Dictionary<TSecond, TFirst> _secondToFirst  = new Dictionary<TSecond, TFirst>();

}

Un poco tarde, pero aquí hay una implementación que escribí hace un tiempo. Maneja algunos casos extremos interesantes, como cuando la clave anula la verificación de igualdad para realizar una igualdad parcial. Esto da como resultado el almacenamiento del diccionario principal A => 1pero el almacenamiento inverso 1 => A'.

Se accede al diccionario inverso a través de la Inversepropiedad.

var map = new BidirectionalDictionary<int, int>();
map.Add(1, 2);
var result = map.Inverse[2]; // result is 1

//
// BidirectionalDictionary.cs
//
// Author:
//   Chris Chilvers <[email protected]>
//
// Copyright (c) 2009 Chris Chilvers
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

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

namespace Cadenza.Collections
{
    public class BidirectionalDictionary<TKey, TValue> : IDictionary<TKey, TValue>
    {
        private readonly IEqualityComparer<TKey> keyComparer;
        private readonly IEqualityComparer<TValue> valueComparer;
        private readonly Dictionary<TKey, TValue> keysToValues;
        private readonly Dictionary<TValue, TKey> valuesToKeys;
        private readonly BidirectionalDictionary<TValue, TKey> inverse;


        public BidirectionalDictionary () : this (10, null, null) {}

        public BidirectionalDictionary (int capacity) : this (capacity, null, null) {}

        public BidirectionalDictionary (IEqualityComparer<TKey> keyComparer, IEqualityComparer<TValue> valueComparer)
            : this (10, keyComparer, valueComparer)
        {
        }

        public BidirectionalDictionary (int capacity, IEqualityComparer<TKey> keyComparer, IEqualityComparer<TValue> valueComparer)
        {
            if (capacity < 0)
                throw new ArgumentOutOfRangeException ("capacity", capacity, "capacity cannot be less than 0");

            this.keyComparer = keyComparer ?? EqualityComparer<TKey>.Default;
            this.valueComparer = valueComparer ?? EqualityComparer<TValue>.Default;

            keysToValues = new Dictionary<TKey, TValue> (capacity, this.keyComparer);
            valuesToKeys = new Dictionary<TValue, TKey> (capacity, this.valueComparer);

            inverse = new BidirectionalDictionary<TValue, TKey> (this);
        }

        private BidirectionalDictionary (BidirectionalDictionary<TValue, TKey> inverse)
        {
            this.inverse = inverse;
            keyComparer = inverse.valueComparer;
            valueComparer = inverse.keyComparer;
            valuesToKeys = inverse.keysToValues;
            keysToValues = inverse.valuesToKeys;
        }


        public BidirectionalDictionary<TValue, TKey> Inverse {
            get { return inverse; }
        }


        public ICollection<TKey> Keys {
            get { return keysToValues.Keys; }
        }

        public ICollection<TValue> Values {
            get { return keysToValues.Values; }
        }

        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator ()
        {
            return keysToValues.GetEnumerator ();
        }

        IEnumerator IEnumerable.GetEnumerator ()
        {
            return GetEnumerator ();
        }

        void ICollection<KeyValuePair<TKey, TValue>>.CopyTo (KeyValuePair<TKey, TValue>[] array, int arrayIndex)
        {
            ((ICollection<KeyValuePair<TKey, TValue>>) keysToValues).CopyTo (array, arrayIndex);
        }


        public bool ContainsKey (TKey key)
        {
            if (key == null)
                throw new ArgumentNullException ("key");
            return keysToValues.ContainsKey (key);
        }

        public bool ContainsValue (TValue value)
        {
            if (value == null)
                throw new ArgumentNullException ("value");
            return valuesToKeys.ContainsKey (value);
        }

        bool ICollection<KeyValuePair<TKey, TValue>>.Contains (KeyValuePair<TKey, TValue> item)
        {
            return ((ICollection<KeyValuePair<TKey, TValue>>) keysToValues).Contains (item);
        }

        public bool TryGetKey (TValue value, out TKey key)
        {
            if (value == null)
                throw new ArgumentNullException ("value");
            return valuesToKeys.TryGetValue (value, out key);
        }

        public bool TryGetValue (TKey key, out TValue value)
        {
            if (key == null)
                throw new ArgumentNullException ("key");
            return keysToValues.TryGetValue (key, out value);
        }

        public TValue this[TKey key] {
            get { return keysToValues [key]; }
            set {
                if (key == null)
                    throw new ArgumentNullException ("key");
                if (value == null)
                    throw new ArgumentNullException ("value");

                //foo[5] = "bar"; foo[6] = "bar"; should not be valid
                //as it would have to remove foo[5], which is unexpected.
                if (ValueBelongsToOtherKey (key, value))
                    throw new ArgumentException ("Value already exists", "value");

                TValue oldValue;
                if (keysToValues.TryGetValue (key, out oldValue)) {
                    // Use the current key for this value to stay consistent
                    // with Dictionary<TKey, TValue> which does not alter
                    // the key if it exists.
                    TKey oldKey = valuesToKeys [oldValue];

                    keysToValues [oldKey] = value;
                    valuesToKeys.Remove (oldValue);
                    valuesToKeys [value] = oldKey;
                } else {
                    keysToValues [key] = value;
                    valuesToKeys [value] = key;
                }
            }
        }

        public int Count {
            get { return keysToValues.Count; }
        }

        bool ICollection<KeyValuePair<TKey, TValue>>.IsReadOnly {
            get { return false; }
        }


        public void Add (TKey key, TValue value)
        {
            if (key == null)
                throw new ArgumentNullException ("key");
            if (value == null)
                throw new ArgumentNullException ("value");

            if (keysToValues.ContainsKey (key))
                throw new ArgumentException ("Key already exists", "key");
            if (valuesToKeys.ContainsKey (value))
                throw new ArgumentException ("Value already exists", "value");

            keysToValues.Add (key, value);
            valuesToKeys.Add (value, key);
        }

        public void Replace (TKey key, TValue value)
        {
            if (key == null)
                throw new ArgumentNullException ("key");
            if (value == null)
                throw new ArgumentNullException ("value");

            // replaces a key value pair, if the key or value already exists those mappings will be replaced.
            // e.g. you have; a -> b, b -> a; c -> d, d -> c
            // you add the mapping; a -> d, d -> a
            // this will remove both of the original mappings
            Remove (key);
            inverse.Remove (value);
            Add (key, value);
        }

        void ICollection<KeyValuePair<TKey, TValue>>.Add (KeyValuePair<TKey, TValue> item)
        {
            Add (item.Key, item.Value);
        }

        public bool Remove (TKey key)
        {
            if (key == null)
                throw new ArgumentNullException ("key");

            TValue value;
            if (keysToValues.TryGetValue (key, out value)) {
                keysToValues.Remove (key);
                valuesToKeys.Remove (value);
                return true;
            }
            else {
                return false;
            }
        }

        bool ICollection<KeyValuePair<TKey, TValue>>.Remove (KeyValuePair<TKey, TValue> item)
        {
            bool removed = ((ICollection<KeyValuePair<TKey, TValue>>) keysToValues).Remove (item);
            if (removed)
                valuesToKeys.Remove (item.Value);
            return removed;
        }

        public void Clear ()
        {
            keysToValues.Clear ();
            valuesToKeys.Clear ();
        }


        private bool ValueBelongsToOtherKey (TKey key, TValue value)
        {
            TKey otherKey;
            if (valuesToKeys.TryGetValue (value, out otherKey))
                // if the keys are not equal the value belongs to another key
                return !keyComparer.Equals (key, otherKey);
            else
                // value doesn't exist in map, thus it cannot belong to another key
                return false;
        }
    }
}

Fuente original y pruebas en github.