multimap in .NET
Because it's almost christmas :)
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// Algorithmia is (c) 2008 Solutions Design. All rights reserved.
// http://www.sd.nl
//////////////////////////////////////////////////////////////////////
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// Copyright (c) 2008 Solutions Design. All rights reserved.
//
// The Algorithmia library sourcecode and its accompanying tools, tests and support code
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// 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<TKey, TValue>"/> 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;
}
}
}
ILookup may be good enough for you - but unfortunately there are no public implementations. You've basically got to go through Enumerable.ToLookup, as far as I'm aware. That means it's a "build once" kind of map - you can't add to it later. However, if that's all you need it's handy to be able to just use the built-in stuff.
In .NET 3.5, there is an ILookup<,> that represents this. The regular implementation (Lookup<,>) is immutable, but I have an EditableLookup<,> in MiscUtil that should do the job nicely.