Question

I need an equivalent to c++’s std::multimap<K, V, Comp, Alloc> in C-sharp. Does it exist in the standard library?

Answer 1

Because it’s almost christmas 🙂

////////////////////////////////////////////////////////////////////// // Algorithmia is (c) 2008 Solutions Design. All rights reserved. // http://www.sd.nl ////////////////////////////////////////////////////////////////////// // COPYRIGHTS: // Copyright (c) 2008 Solutions Design. All rights reserved. //  // The Algorithmia library sourcecode and its accompanying tools, tests and support code // are released under the following license: (BSD2) // ---------------------------------------------------------------------- // Redistribution and use in source and binary forms, with or without modification,  // are permitted provided that the following conditions are met:  // // 1) Redistributions of source code must retain the above copyright notice, this list of  //    conditions and the following disclaimer.  // 2) Redistributions in binary form must reproduce the above copyright notice, this list of  //    conditions and the following disclaimer in the documentation and/or other materials  //    provided with the distribution.  //  // THIS SOFTWARE IS PROVIDED BY SOLUTIONS DESIGN ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,  // INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A  // PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SOLUTIONS DESIGN OR CONTRIBUTORS BE LIABLE FOR  // ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT  // NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR  // BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,  // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE  // USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  // // The views and conclusions contained in the software and documentation are those of the authors  // and should not be interpreted as representing official policies, either expressed or implied,  // of Solutions Design.  // ////////////////////////////////////////////////////////////////////// // Contributers to the code: //      - Frans  Bouma [FB] ////////////////////////////////////////////////////////////////////// using System; using System.Collections.Generic; using System.Linq; using System.Text; using SD.Tools.Algorithmia.UtilityClasses;  namespace SD.Tools.Algorithmia.GeneralDataStructures {     /// <summary>     /// Extension to the normal Dictionary. This class can store more than one value for every key. It keeps a HashSet for every Key value.     /// Calling Add with the same Key and multiple values will store each value under the same Key in the Dictionary. Obtaining the values     /// for a Key will return the HashSet with the Values of the Key.      /// </summary>     /// <typeparam name='TKey'>The type of the key.</typeparam>     /// <typeparam name='TValue'>The type of the value.</typeparam>     public class MultiValueDictionary<TKey, TValue> : Dictionary<TKey, HashSet<TValue>>     {         /// <summary>         /// Initializes a new instance of the <see cref='MultiValueDictionary&lt;TKey, TValue&gt;'/> class.         /// </summary>         public MultiValueDictionary()             : base()         {         }           /// <summary>         /// Adds the specified value under the specified key         /// </summary>         /// <param name='key'>The key.</param>         /// <param name='value'>The value.</param>         public void Add(TKey key, TValue value)         {             ArgumentVerifier.CantBeNull(key, 'key');              HashSet<TValue> container = null;             if(!this.TryGetValue(key, out container))             {                 container = new HashSet<TValue>();                 base.Add(key, container);             }             container.Add(value);         }           /// <summary>         /// Determines whether this dictionary contains the specified value for the specified key          /// </summary>         /// <param name='key'>The key.</param>         /// <param name='value'>The value.</param>         /// <returns>true if the value is stored for the specified key in this dictionary, false otherwise</returns>         public bool ContainsValue(TKey key, TValue value)         {             ArgumentVerifier.CantBeNull(key, 'key');             bool toReturn = false;             HashSet<TValue> values = null;             if(this.TryGetValue(key, out values))             {                 toReturn = values.Contains(value);             }             return toReturn;         }           /// <summary>         /// Removes the specified value for the specified key. It will leave the key in the dictionary.         /// </summary>         /// <param name='key'>The key.</param>         /// <param name='value'>The value.</param>         public void Remove(TKey key, TValue value)         {             ArgumentVerifier.CantBeNull(key, 'key');              HashSet<TValue> container = null;             if(this.TryGetValue(key, out container))             {                 container.Remove(value);                 if(container.Count <= 0)                 {                     this.Remove(key);                 }             }         }           /// <summary>         /// Merges the specified multivaluedictionary into this instance.         /// </summary>         /// <param name='toMergeWith'>To merge with.</param>         public void Merge(MultiValueDictionary<TKey, TValue> toMergeWith)         {              if(toMergeWith==null)             {                 return;             }              foreach(KeyValuePair<TKey, HashSet<TValue>> pair in toMergeWith)             {                 foreach(TValue value in pair.Value)                 {                     this.Add(pair.Key, value);                 }             }         }           /// <summary>         /// Gets the values for the key specified. This method is useful if you want to avoid an exception for key value retrieval and you can't use TryGetValue         /// (e.g. in lambdas)         /// </summary>         /// <param name='key'>The key.</param>         /// <param name='returnEmptySet'>if set to true and the key isn't found, an empty hashset is returned, otherwise, if the key isn't found, null is returned</param>         /// <returns>         /// This method will return null (or an empty set if returnEmptySet is true) if the key wasn't found, or         /// the values if key was found.         /// </returns>         public HashSet<TValue> GetValues(TKey key, bool returnEmptySet)         {             HashSet<TValue> toReturn = null;             if(!base.TryGetValue(key, out toReturn) && returnEmptySet)             {                 toReturn = new HashSet<TValue>();             }             return toReturn;         }     } }