Generic form of NameValueCollection in .Net

Generic form of NameValueCollection in .Net - c#

Does .Net provides generic form of NameValueCollection or an alternative to
Dictionary<string,List<T>> ?
Something like
Person john = new Person();
...
Person vick = new Person();
...
NameValueCollection<Person> stringToPerson = new NameValueCollection<Person>();
stringToPerson.Add("John",john)
stringToPerson.Add("Vick",vick)
Actually in my case am forced to rely on Dictionary<string,List<Peron>>, is there any other alternative?
Regards,
Jeez

There's no such thing built in to the BCL as far as I know. I would just write your own class which wraps a Dictionary<string, List<T>> internally and exposes appropriate methods (e.g., Add could add an element to the List<T> for the given key).
For example:
class NameValueCollection<T>
{
Dictionary<string, List<T>> _dict = new Dictionary<string, List<T>>();
public void Add(string name, T value)
{
List<T> list;
if (!_dict.TryGetValue(name, out list))
{
_dict[name] = list = new List<T>();
}
list.Add(value);
}
// etc.
}

The closest alternative is probably the ILookup<TKey, TElement> interface. At the moment, the only public type that implements it in the BCL is the immutable Lookup<TKey, TElement> class, an instance of which can be created with the Enumerable.ToLookup method. If you want a mutable type that implements the interface, you'll have to write one yourself; you can find an example implementation here.
In your case, you probably want an ILookup<string, Person>.

Oh, I see what you want to do now. You want to be able to add to the Person collection without having to create a new List each time. Extension methods to the rescue!
public static void SafeAdd<TValue>(this IDictionary<TKey, ICollection<TValue>> dict, TKey key, TValue value)
{
HashSet<T> container;
if (!dict.TryGetValue(key, out container))
{
dict[key] = new HashSet<TValue>();
}
dict[key].Add(value);
}
Usage:
var names = new Dictionary<string, ICollection<Person>>();
names.SafeAdd("John", new Person("John"));

Nothing inbuilt; there is Lookup<TKey,TValue> which operates as a multi-map, but that is immutable. I wrote a mutable EditableLookup<TKey,TValue> for MiscUtil which may help.

Generic NameValueCollection
What makes NameValueCollection special unlike Dictionary, is that one key can contain several elements.
The generic NameValueCollection<T> based on NameObjectCollectionBase is in the following code:
using System.Collections.Specialized;
namespace System.Collections.Generic
{
public class NameValueCollection<T> : NameObjectCollectionBase
{
private string[] _keys; // Cached keys.
private T[] _values; // Cached values.
// Resets the caches.
protected void InvalidateCachedArrays()
{
_values = null;
_keys = null;
}
// Converts ArrayLit to Array of T elements.
protected static T[] AsArray(ArrayList list)
{
int count = 0;
if (list == null || (count = list.Count) == 0)
return (T[])null;
T[] array = new T[count];
list.CopyTo(0, array, 0, count);
return array;
}
// Gets all values cache.
protected ArrayList GetAllValues()
{
int count = Count;
ArrayList arrayList = new ArrayList(count);
for (int i = 0; i < count; ++i)
{
arrayList.AddRange(Get(i));
}
return arrayList;
}
// Adds single value to collection.
public void Add(string name, T value)
{
InvalidateCachedArrays();
ArrayList arrayList = (ArrayList)BaseGet(name);
if (arrayList == null)
{
arrayList = new ArrayList(1);
if (value != null) arrayList.Add(value);
BaseAdd(name, arrayList);
}
else
{
if (value == null) return;
arrayList.Add(value);
}
}
// Adds range of values to collection.
public void Add(NameValueCollection<T> collection)
{
InvalidateCachedArrays();
int count = collection.Count;
for (int i = 0; i < count; i++)
{
string key = collection.GetKey(i);
T[] values = collection.Get(i);
foreach (var value in values)
{
Add(key, value);
}
}
}
// Set single value (prevoious values will be removed).
public void Set(string name, T value)
{
InvalidateCachedArrays();
BaseSet(name, new ArrayList(1) { value });
}
// Set range of values (prevoious values will be removed).
public void Set(string name, params T[] values)
{
InvalidateCachedArrays();
BaseSet(name, new ArrayList(values));
}
// Gets all values that paired with specified key.
public T[] Get(string name)
{
return AsArray((ArrayList)BaseGet(name));
}
// Gets all values at the specified index of collection.
public T[] Get(int index)
{
return AsArray((ArrayList)BaseGet(index));
}
// Gets string containing the key at the specified index.
public string GetKey(int index)
{
return BaseGetKey(index);
}
// Removes values from the specified key.
public void Remove(string name)
{
InvalidateCachedArrays();
BaseRemove(name);
}
// Removes all data from the collection.
public void Clear()
{
InvalidateCachedArrays();
BaseClear();
}
// All keys that the current collection contains.
public new string[] Keys
{
get
{
if (_keys == null)
_keys = BaseGetAllKeys();
return _keys;
}
}
// All values that the current collection contains.
public T[] Values
{
get
{
if (_values == null)
_values = AsArray(GetAllValues());
return _values;
}
}
// Values at the specefied index.
public T[] this[int index]
{
get
{
return Get(index);
}
set
{
BaseSet(index, new ArrayList(value));
}
}
// Values at the specefied key.
public T[] this[string name]
{
get
{
return Get(name);
}
set
{
BaseSet(name, new ArrayList(value));
}
}
// Enumerates all entries.
public IEnumerable<KeyValuePair<string, T>> GetAllEntries()
{
foreach (string key in Keys)
{
foreach (T value in Get(key))
{
yield return new KeyValuePair<string, T>(key, value);
}
}
}
}
}
Usage:
NameValueCollection<int> collection = new NameValueCollection<int>();
collection.Add("a", 123);
collection.Add("a", 456); // 123 and 456 will be inserted into the same key.
collection.Add("b", 789); // 789 will be inserted into another key.
int[] a = collection.Get("a"); // contains 123 and 456.
int[] b = collection.Get("b"); // contains 789.
The above code implements the main features.
Here is complete implementation of the NameValueCollection<T> with additional tools.

Related

C# - Dictionary with Behaviour of a Ring List?

I need a ring list dictionary that can store key and item. Capacity = 50 and when I add #51 the first item must be removed. Basically it must be a dictionary that behaves like a ring list.
Is there something in .NET Framework that can do that ? Or do I have to write it by myself ?

You won't find anything built-in I think but you can easily implement one using OrderedDictionary
OrderedDictionary maintains items in order which they are inserted. Whenever you reach the limit/capacity you can remove the first item.

or use an extension method :
EDIT :
because
latest added entry ends up being returned first.
so
u can remove the first item like :
dictionary.Remove(dictionary.Last().Key);
& so your extension method is :
addExtension(this Dictionary<string, object> dictionary, string key, object value)
{
if(dictionary.Count == 50)
dictionary.Remove(dictionary.Last().Key);
dictionary.Add(key, value);
}

Try this:
class Program
{
static void Main(string[] args)
{
var rD = new RingDictionary(50);
for (int i = 0; i < 75; i++)
{
rD.Add(i, i);
}
foreach (var item in rD.Keys)
{
Console.WriteLine("{0} {1}", item, rD[item]);
}
}
}
class RingDictionary : OrderedDictionary
{
int indexKey;
int _capacity = 0;
public int Capacity
{
get { return _capacity; }
set
{
if (value <= 0)
{
var errorMessage = typeof(Environment)
.GetMethod(
"GetResourceString",
System.Reflection.BindingFlags.Static |
System.Reflection.BindingFlags.NonPublic,
null,
new Type[] { typeof(string) },
null)
.Invoke(null, new object[] {
"ArgumentOutOfRange_NegativeCapacity"
}).ToString();
throw new ArgumentException(errorMessage);
}
_capacity = value;
}
}
public RingDictionary(int capacity)
{
indexKey = -1;
Capacity = capacity;
}
public new void Add(object key, object value)
{
indexKey++;
if (base.Keys.Count > _capacity)
{
for (int i = base.Keys.Count-1; i >Capacity-1 ; i--)
{
base.RemoveAt(i);
}
}
if (base.Keys.Count == _capacity)
{
base.RemoveAt(indexKey % _capacity);
base.Insert(indexKey % _capacity, key, value);
}
else
{
base.Add(key, value);
}
}
}

Collection that allows only unique items in .NET?

Is there a collection in C# that will not let you add duplicate items to it? For example, with the silly class of
public class Customer {
public string FirstName { get; set; }
public string LastName { get; set; }
public string Address { get; set; }
public override int GetHashCode() {
return (FirstName + LastName + Address).GetHashCode();
}
public override bool Equals(object obj) {
Customer C = obj as Customer;
return C != null && String.Equals(this.FirstName, C.FirstName) && String.Equals(this.LastName, C.LastName) && String.Equals(this.Address, C.Address);
}
}
The following code will (obviously) throw an exception:
Customer Adam = new Customer { Address = "A", FirstName = "Adam", LastName = "" };
Customer AdamDup = new Customer { Address = "A", FirstName = "Adam", LastName = "" };
Dictionary<Customer, bool> CustomerHash = new Dictionary<Customer, bool>();
CustomerHash.Add(Adam, true);
CustomerHash.Add(AdamDup, true);
But is there a class that will similarly guarantee uniqueness, but without KeyValuePairs? I thought HashSet<T> would do that, but having read the docs it seems that class is just a set implementation (go figure).

HashSet<T> is what you're looking for. From MSDN (emphasis added):
The HashSet<T> class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.
Note that the HashSet<T>.Add(T item) method returns a bool -- true if the item was added to the collection; false if the item was already present.

How about just an extension method on HashSet?
public static void AddOrThrow<T>(this HashSet<T> hash, T item)
{
if (!hash.Add(item))
throw new ValueExistingException();
}

From the HashSet<T> page on MSDN:
The HashSet(Of T) class provides high-performance set operations. A set is a collection that contains no duplicate elements, and whose elements are in no particular order.
(emphasis mine)

If all you need is to ensure uniqueness of elements, then HashSet is what you need.
What do you mean when you say "just a set implementation"? A set is (by definition) a collection of unique elements that doesn't save element order.

Just to add my 2 cents...
if you need a ValueExistingException-throwing HashSet<T> you can also create your collection easily:
public class ThrowingHashSet<T> : ICollection<T>
{
private HashSet<T> innerHash = new HashSet<T>();
public void Add(T item)
{
if (!innerHash.Add(item))
throw new ValueExistingException();
}
public void Clear()
{
innerHash.Clear();
}
public bool Contains(T item)
{
return innerHash.Contains(item);
}
public void CopyTo(T[] array, int arrayIndex)
{
innerHash.CopyTo(array, arrayIndex);
}
public int Count
{
get { return innerHash.Count; }
}
public bool IsReadOnly
{
get { return false; }
}
public bool Remove(T item)
{
return innerHash.Remove(item);
}
public IEnumerator<T> GetEnumerator()
{
return innerHash.GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
}
this can be useful for example if you need it in many places...

You can try HashSet<T>

You may look into something kind of Unique List as follows
public class UniqueList<T>
{
public List<T> List
{
get;
private set;
}
List<T> _internalList;
public static UniqueList<T> NewList
{
get
{
return new UniqueList<T>();
}
}
private UniqueList()
{
_internalList = new List<T>();
List = new List<T>();
}
public void Add(T value)
{
List.Clear();
_internalList.Add(value);
List.AddRange(_internalList.Distinct());
//return List;
}
public void Add(params T[] values)
{
List.Clear();
_internalList.AddRange(values);
List.AddRange(_internalList.Distinct());
// return List;
}
public bool Has(T value)
{
return List.Contains(value);
}
}
and you can use it like follows
var uniquelist = UniqueList<string>.NewList;
uniquelist.Add("abc","def","ghi","jkl","mno");
uniquelist.Add("abc","jkl");
var _myList = uniquelist.List;
will only return "abc","def","ghi","jkl","mno" always even when duplicates are added to it

As an overall check different methods here are 4 ways to check if the collection has not any duplicates:
public static bool LinqAny<T>(IEnumerable<T> enumerable)
{
HashSet<T> set = new();
return enumerable.Any(element => !set.Add(element));
}
public static bool LinqAll<T>(IEnumerable<T> enumerable)
{
HashSet<T> set = new();
return !enumerable.All(set.Add);
}
public static bool LinqDistinct<T>(IEnumerable<T> enumerable)
{
return enumerable.Distinct().Count() != enumerable.Count();
}
public static bool ToHashSet<T>(IEnumerable<T> enumerable)
{
return enumerable.ToHashSet().Count != enumerable.Count();
}

SortList duplicated key, but it shouldn't

I have a class which implements IList interface. I requires a "sorted view" of this list, but without modifying it (I cannot sort directly the IList class).
These view shall be updated when the original list is modified, keeping items sorted. So, I've introduced a SortList creation method which create a SortList which has a comparer for the specific object contained in the original list.
Here is the snippet of code:
public class MyList<T> : ICollection, IList<T>
{
public SortedList CreateSortView(string property)
{
try
{
Lock();
SortListView sortView;
if (mSortListViews.ContainsKey(property) == false)
{
// Create sorted view
sortView = new SortListView(property, Count);
mSortListViews.Add(property, sortView);
foreach (T item in Items)
sortView.Add(item);
} else
sortView = mSortListViews[property];
sortView.ReferenceCount++;
return (sortView);
}
finally
{
Unlock();
}
}
public void DeleteSortView(string property)
{
try
{
Lock();
// Unreference sorted view
mSortListViews[property].ReferenceCount--;
// Remove sorted view
if (mSortListViews[property].ReferenceCount == 0)
mSortListViews.Remove(property);
}
finally
{
Unlock();
}
}
protected class SortListView : SortedList
{
public SortListView(string property, int capacity)
: base(new GenericPropertyComparer(typeof(T).GetProperty(property, BindingFlags.Instance | BindingFlags.Public)), capacity)
{
}
public int ReferenceCount = 0;
public void Add(T item)
{
Add(item, item);
}
public void Remove(T item)
{
base.Remove(item);
}
class GenericPropertyComparer : IComparer
{
public GenericPropertyComparer(PropertyInfo property)
{
if (property == null)
throw new ArgumentException("property doesn't specify a valid property");
if (property.CanRead == false)
throw new ArgumentException("property specify a write-only property");
if (property.PropertyType.GetInterface("IComparable") == null)
throw new ArgumentException("property type doesn't IComparable");
mSortingProperty = property;
}
public int Compare(object x, object y)
{
IComparable propX = (IComparable)mSortingProperty.GetValue(x, null);
IComparable propY = (IComparable)mSortingProperty.GetValue(y, null);
return (propX.CompareTo(propY));
}
private PropertyInfo mSortingProperty = null;
}
private Dictionary<string, SortListView> mSortListViews = new Dictionary<string, SortListView>();
}
Practically, class users request to create a SortListView specifying the name of property which determine the sorting, and using the reflection each SortListView defined a IComparer which keep sorted the items.
Whenever an item is added or removed from the original list, every created SortListView will be updated with the same operation.
This seems good at first chance, but it creates me problems since it give me the following exception when adding items to the SortList:
System.ArgumentException: Item has already been added. Key in dictionary: 'PowerShell_ISE [C:\Windows\sysWOW64\WindowsPowerShell\v1.0\PowerShell_ISE.exe]' Key being added: 'PowerShell_ISE [C:\Windows\system32\WindowsPowerShell\v1.0\PowerShell_ISE.exe]'
As you can see from the exception message, thrown by SortedListView.Add(object), the string representation of the key (the list item object) is different (note the path of the executable).
Why SortList give me that exception?
To solve this I tried to implement a GetHashCode() for the underlying object, but without success:
public override int GetHashCode()
{
return (
base.GetHashCode() ^
mApplicationName.GetHashCode() ^
mApplicationPath.GetHashCode() ^
mCommandLine.GetHashCode() ^
mWorkingDirectory.GetHashCode()
);
}

If I understood you correctly, your purpose is just to get a view of you list, sorted by a property of the object.
Then, why use SortedList that requires unique Keys, when you could easily get your result using LINQ OrderBy (or if you're using .net 2.0 List.Sort()) ?
Hence, for example, your CreateSortView could be implemented in this way:
(omitting lock, try/finally and reference counting)
public IList<T> CreateSortView(string property)
{
IList<T> sortView;
if (mSortListViews.ContainsKey(property) == false)
{
// Create sorted view
sortView = this.OrderBy(x => x, new GenericPropertyComparer<T>(property)).ToList();
mSortListViews.Add(property, sortView);
}
else
{
sortView = mSortListViews[property];
}
return sortView;
}
With GenericPropertyComparer implemented as follows:
class GenericPropertyComparer<T> : IComparer<T>
{
public GenericPropertyComparer(string propertyName)
{
var property = typeof(T).GetProperty(propertyName, BindingFlags.Instance | BindingFlags.Public);
if (property == null)
throw new ArgumentException("property doesn't specify a valid property");
if (property.CanRead == false)
throw new ArgumentException("property specify a write-only property");
if (property.PropertyType.GetInterface("IComparable") == null)
throw new ArgumentException("property type doesn't IComparable");
mSortingProperty = property;
}
public int Compare(T x, T y)
{
IComparable propX = (IComparable)mSortingProperty.GetValue(x, null);
IComparable propY = (IComparable)mSortingProperty.GetValue(y, null);
return (propX.CompareTo(propY));
}
private PropertyInfo mSortingProperty = null;
}
EDIT:
If you need to add/remove items from your sorted collection frequeltly, maybe use a SortedList would be better, but the problem with SortedList is that it needs unique keys, and in your case you can't assure that.
Anyway, you can use a custom sorted List that doesn't need unique values, look at the link below for a simple implementation:
Implementation of sorted IList<T> that doesn't require unique values

It seems to me it is a multithreading issue. I can't see what the Lock() function is doing in your code, but I think you will have more luck by surrounding the dictionary access code with a standard lock:
lock(this){
SortListView sortView;
if (mSortListViews.ContainsKey(property) == false) {
// Create sorted view
sortView = new SortListView(property, Count);
mSortListViews.Add(property, sortView);
foreach (T item in Items)
sortView.Add(item);
} else
sortView = mSortListViews[property];
sortView.ReferenceCount++;
}
and the same in the removing part.

Thanks to digEmAll's comment, I found a quick solution: The IComparer implementation shall return 0 only on objects really equals!
So:
public int Compare(object x, object y)
{
IComparable propX = (IComparable)mSortingProperty.GetValue(x, null);
IComparable propY = (IComparable)mSortingProperty.GetValue(y, null);
int compare;
if ((compare = propX.CompareTo(propY)) == 0) {
if (x.GetHashCode() < y.GetHashCode())
return (-1);
else if (x.GetHashCode() > y.GetHashCode())
return (+1);
else return (0);
} else
return (compare);
}

Why no generic implementation of OrderedDictionary? [duplicate]

There doesn't appear to be a generic implementation of OrderedDictionary (which is in the System.Collections.Specialized namespace) in .NET 3.5. Is there one that I'm missing?
I've found implementations out there to provide the functionality, but wondered if/why there isn't a generic implementation out-of-the-box and if anyone knows whether it's something in .NET 4.0?

Implementing a generic OrderedDictionary isn't terribly difficult, but it's unnecessarily time consuming and frankly this class is a huge oversight on Microsoft's part. There are multiple ways of implementing this, but I chose to use a KeyedCollection for my internal storage. I also chose to implement various methods for sorting the way that List<T> does since this is essentially a hybrid IList and IDictionary. I've included my implementation here for posterity.
Here's the interface. Notice that it includes System.Collections.Specialized.IOrderedDictionary, which is the non-generic version of this interface that was provided by Microsoft.
// http://unlicense.org
using System;
using System.Collections.Generic;
using System.Collections.Specialized;
namespace mattmc3.Common.Collections.Generic {
public interface IOrderedDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IOrderedDictionary {
new TValue this[int index] { get; set; }
new TValue this[TKey key] { get; set; }
new int Count { get; }
new ICollection<TKey> Keys { get; }
new ICollection<TValue> Values { get; }
new void Add(TKey key, TValue value);
new void Clear();
void Insert(int index, TKey key, TValue value);
int IndexOf(TKey key);
bool ContainsValue(TValue value);
bool ContainsValue(TValue value, IEqualityComparer<TValue> comparer);
new bool ContainsKey(TKey key);
new IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator();
new bool Remove(TKey key);
new void RemoveAt(int index);
new bool TryGetValue(TKey key, out TValue value);
TValue GetValue(TKey key);
void SetValue(TKey key, TValue value);
KeyValuePair<TKey, TValue> GetItem(int index);
void SetItem(int index, TValue value);
}
}
Here's the implementation along with helper classes:
// http://unlicense.org
using System;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Collections;
using System.Collections.Specialized;
using System.Collections.Generic;
using System.Linq;
namespace mattmc3.Common.Collections.Generic {
/// <summary>
/// A dictionary object that allows rapid hash lookups using keys, but also
/// maintains the key insertion order so that values can be retrieved by
/// key index.
/// </summary>
public class OrderedDictionary<TKey, TValue> : IOrderedDictionary<TKey, TValue> {
#region Fields/Properties
private KeyedCollection2<TKey, KeyValuePair<TKey, TValue>> _keyedCollection;
/// <summary>
/// Gets or sets the value associated with the specified key.
/// </summary>
/// <param name="key">The key associated with the value to get or set.</param>
public TValue this[TKey key] {
get {
return GetValue(key);
}
set {
SetValue(key, value);
}
}
/// <summary>
/// Gets or sets the value at the specified index.
/// </summary>
/// <param name="index">The index of the value to get or set.</param>
public TValue this[int index] {
get {
return GetItem(index).Value;
}
set {
SetItem(index, value);
}
}
public int Count {
get { return _keyedCollection.Count; }
}
public ICollection<TKey> Keys {
get {
return _keyedCollection.Select(x => x.Key).ToList();
}
}
public ICollection<TValue> Values {
get {
return _keyedCollection.Select(x => x.Value).ToList();
}
}
public IEqualityComparer<TKey> Comparer {
get;
private set;
}
#endregion
#region Constructors
public OrderedDictionary() {
Initialize();
}
public OrderedDictionary(IEqualityComparer<TKey> comparer) {
Initialize(comparer);
}
public OrderedDictionary(IOrderedDictionary<TKey, TValue> dictionary) {
Initialize();
foreach (KeyValuePair<TKey, TValue> pair in dictionary) {
_keyedCollection.Add(pair);
}
}
public OrderedDictionary(IOrderedDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer) {
Initialize(comparer);
foreach (KeyValuePair<TKey, TValue> pair in dictionary) {
_keyedCollection.Add(pair);
}
}
#endregion
#region Methods
private void Initialize(IEqualityComparer<TKey> comparer = null) {
this.Comparer = comparer;
if (comparer != null) {
_keyedCollection = new KeyedCollection2<TKey, KeyValuePair<TKey, TValue>>(x => x.Key, comparer);
}
else {
_keyedCollection = new KeyedCollection2<TKey, KeyValuePair<TKey, TValue>>(x => x.Key);
}
}
public void Add(TKey key, TValue value) {
_keyedCollection.Add(new KeyValuePair<TKey, TValue>(key, value));
}
public void Clear() {
_keyedCollection.Clear();
}
public void Insert(int index, TKey key, TValue value) {
_keyedCollection.Insert(index, new KeyValuePair<TKey, TValue>(key, value));
}
public int IndexOf(TKey key) {
if (_keyedCollection.Contains(key)) {
return _keyedCollection.IndexOf(_keyedCollection[key]);
}
else {
return -1;
}
}
public bool ContainsValue(TValue value) {
return this.Values.Contains(value);
}
public bool ContainsValue(TValue value, IEqualityComparer<TValue> comparer) {
return this.Values.Contains(value, comparer);
}
public bool ContainsKey(TKey key) {
return _keyedCollection.Contains(key);
}
public KeyValuePair<TKey, TValue> GetItem(int index) {
if (index < 0 || index >= _keyedCollection.Count) {
throw new ArgumentException(String.Format("The index was outside the bounds of the dictionary: {0}", index));
}
return _keyedCollection[index];
}
/// <summary>
/// Sets the value at the index specified.
/// </summary>
/// <param name="index">The index of the value desired</param>
/// <param name="value">The value to set</param>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown when the index specified does not refer to a KeyValuePair in this object
/// </exception>
public void SetItem(int index, TValue value) {
if (index < 0 || index >= _keyedCollection.Count) {
throw new ArgumentException("The index is outside the bounds of the dictionary: {0}".FormatWith(index));
}
var kvp = new KeyValuePair<TKey, TValue>(_keyedCollection[index].Key, value);
_keyedCollection[index] = kvp;
}
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator() {
return _keyedCollection.GetEnumerator();
}
public bool Remove(TKey key) {
return _keyedCollection.Remove(key);
}
public void RemoveAt(int index) {
if (index < 0 || index >= _keyedCollection.Count) {
throw new ArgumentException(String.Format("The index was outside the bounds of the dictionary: {0}", index));
}
_keyedCollection.RemoveAt(index);
}
/// <summary>
/// Gets the value associated with the specified key.
/// </summary>
/// <param name="key">The key associated with the value to get.</param>
public TValue GetValue(TKey key) {
if (_keyedCollection.Contains(key) == false) {
throw new ArgumentException("The given key is not present in the dictionary: {0}".FormatWith(key));
}
var kvp = _keyedCollection[key];
return kvp.Value;
}
/// <summary>
/// Sets the value associated with the specified key.
/// </summary>
/// <param name="key">The key associated with the value to set.</param>
/// <param name="value">The the value to set.</param>
public void SetValue(TKey key, TValue value) {
var kvp = new KeyValuePair<TKey, TValue>(key, value);
var idx = IndexOf(key);
if (idx > -1) {
_keyedCollection[idx] = kvp;
}
else {
_keyedCollection.Add(kvp);
}
}
public bool TryGetValue(TKey key, out TValue value) {
if (_keyedCollection.Contains(key)) {
value = _keyedCollection[key].Value;
return true;
}
else {
value = default(TValue);
return false;
}
}
#endregion
#region sorting
public void SortKeys() {
_keyedCollection.SortByKeys();
}
public void SortKeys(IComparer<TKey> comparer) {
_keyedCollection.SortByKeys(comparer);
}
public void SortKeys(Comparison<TKey> comparison) {
_keyedCollection.SortByKeys(comparison);
}
public void SortValues() {
var comparer = Comparer<TValue>.Default;
SortValues(comparer);
}
public void SortValues(IComparer<TValue> comparer) {
_keyedCollection.Sort((x, y) => comparer.Compare(x.Value, y.Value));
}
public void SortValues(Comparison<TValue> comparison) {
_keyedCollection.Sort((x, y) => comparison(x.Value, y.Value));
}
#endregion
#region IDictionary<TKey, TValue>
void IDictionary<TKey, TValue>.Add(TKey key, TValue value) {
Add(key, value);
}
bool IDictionary<TKey, TValue>.ContainsKey(TKey key) {
return ContainsKey(key);
}
ICollection<TKey> IDictionary<TKey, TValue>.Keys {
get { return Keys; }
}
bool IDictionary<TKey, TValue>.Remove(TKey key) {
return Remove(key);
}
bool IDictionary<TKey, TValue>.TryGetValue(TKey key, out TValue value) {
return TryGetValue(key, out value);
}
ICollection<TValue> IDictionary<TKey, TValue>.Values {
get { return Values; }
}
TValue IDictionary<TKey, TValue>.this[TKey key] {
get {
return this[key];
}
set {
this[key] = value;
}
}
#endregion
#region ICollection<KeyValuePair<TKey, TValue>>
void ICollection<KeyValuePair<TKey, TValue>>.Add(KeyValuePair<TKey, TValue> item) {
_keyedCollection.Add(item);
}
void ICollection<KeyValuePair<TKey, TValue>>.Clear() {
_keyedCollection.Clear();
}
bool ICollection<KeyValuePair<TKey, TValue>>.Contains(KeyValuePair<TKey, TValue> item) {
return _keyedCollection.Contains(item);
}
void ICollection<KeyValuePair<TKey, TValue>>.CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex) {
_keyedCollection.CopyTo(array, arrayIndex);
}
int ICollection<KeyValuePair<TKey, TValue>>.Count {
get { return _keyedCollection.Count; }
}
bool ICollection<KeyValuePair<TKey, TValue>>.IsReadOnly {
get { return false; }
}
bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item) {
return _keyedCollection.Remove(item);
}
#endregion
#region IEnumerable<KeyValuePair<TKey, TValue>>
IEnumerator<KeyValuePair<TKey, TValue>> IEnumerable<KeyValuePair<TKey, TValue>>.GetEnumerator() {
return GetEnumerator();
}
#endregion
#region IEnumerable
IEnumerator IEnumerable.GetEnumerator() {
return GetEnumerator();
}
#endregion
#region IOrderedDictionary
IDictionaryEnumerator IOrderedDictionary.GetEnumerator() {
return new DictionaryEnumerator<TKey, TValue>(this);
}
void IOrderedDictionary.Insert(int index, object key, object value) {
Insert(index, (TKey)key, (TValue)value);
}
void IOrderedDictionary.RemoveAt(int index) {
RemoveAt(index);
}
object IOrderedDictionary.this[int index] {
get {
return this[index];
}
set {
this[index] = (TValue)value;
}
}
#endregion
#region IDictionary
void IDictionary.Add(object key, object value) {
Add((TKey)key, (TValue)value);
}
void IDictionary.Clear() {
Clear();
}
bool IDictionary.Contains(object key) {
return _keyedCollection.Contains((TKey)key);
}
IDictionaryEnumerator IDictionary.GetEnumerator() {
return new DictionaryEnumerator<TKey, TValue>(this);
}
bool IDictionary.IsFixedSize {
get { return false; }
}
bool IDictionary.IsReadOnly {
get { return false; }
}
ICollection IDictionary.Keys {
get { return (ICollection)this.Keys; }
}
void IDictionary.Remove(object key) {
Remove((TKey)key);
}
ICollection IDictionary.Values {
get { return (ICollection)this.Values; }
}
object IDictionary.this[object key] {
get {
return this[(TKey)key];
}
set {
this[(TKey)key] = (TValue)value;
}
}
#endregion
#region ICollection
void ICollection.CopyTo(Array array, int index) {
((ICollection)_keyedCollection).CopyTo(array, index);
}
int ICollection.Count {
get { return ((ICollection)_keyedCollection).Count; }
}
bool ICollection.IsSynchronized {
get { return ((ICollection)_keyedCollection).IsSynchronized; }
}
object ICollection.SyncRoot {
get { return ((ICollection)_keyedCollection).SyncRoot; }
}
#endregion
}
public class KeyedCollection2<TKey, TItem> : KeyedCollection<TKey, TItem> {
private const string DelegateNullExceptionMessage = "Delegate passed cannot be null";
private Func<TItem, TKey> _getKeyForItemDelegate;
public KeyedCollection2(Func<TItem, TKey> getKeyForItemDelegate)
: base() {
if (getKeyForItemDelegate == null) throw new ArgumentNullException(DelegateNullExceptionMessage);
_getKeyForItemDelegate = getKeyForItemDelegate;
}
public KeyedCollection2(Func<TItem, TKey> getKeyForItemDelegate, IEqualityComparer<TKey> comparer)
: base(comparer) {
if (getKeyForItemDelegate == null) throw new ArgumentNullException(DelegateNullExceptionMessage);
_getKeyForItemDelegate = getKeyForItemDelegate;
}
protected override TKey GetKeyForItem(TItem item) {
return _getKeyForItemDelegate(item);
}
public void SortByKeys() {
var comparer = Comparer<TKey>.Default;
SortByKeys(comparer);
}
public void SortByKeys(IComparer<TKey> keyComparer) {
var comparer = new Comparer2<TItem>((x, y) => keyComparer.Compare(GetKeyForItem(x), GetKeyForItem(y)));
Sort(comparer);
}
public void SortByKeys(Comparison<TKey> keyComparison) {
var comparer = new Comparer2<TItem>((x, y) => keyComparison(GetKeyForItem(x), GetKeyForItem(y)));
Sort(comparer);
}
public void Sort() {
var comparer = Comparer<TItem>.Default;
Sort(comparer);
}
public void Sort(Comparison<TItem> comparison) {
var newComparer = new Comparer2<TItem>((x, y) => comparison(x, y));
Sort(newComparer);
}
public void Sort(IComparer<TItem> comparer) {
List<TItem> list = base.Items as List<TItem>;
if (list != null) {
list.Sort(comparer);
}
}
}
public class Comparer2<T> : Comparer<T> {
//private readonly Func<T, T, int> _compareFunction;
private readonly Comparison<T> _compareFunction;
#region Constructors
public Comparer2(Comparison<T> comparison) {
if (comparison == null) throw new ArgumentNullException("comparison");
_compareFunction = comparison;
}
#endregion
public override int Compare(T arg1, T arg2) {
return _compareFunction(arg1, arg2);
}
}
public class DictionaryEnumerator<TKey, TValue> : IDictionaryEnumerator, IDisposable {
readonly IEnumerator<KeyValuePair<TKey, TValue>> impl;
public void Dispose() { impl.Dispose(); }
public DictionaryEnumerator(IDictionary<TKey, TValue> value) {
this.impl = value.GetEnumerator();
}
public void Reset() { impl.Reset(); }
public bool MoveNext() { return impl.MoveNext(); }
public DictionaryEntry Entry {
get {
var pair = impl.Current;
return new DictionaryEntry(pair.Key, pair.Value);
}
}
public object Key { get { return impl.Current.Key; } }
public object Value { get { return impl.Current.Value; } }
public object Current { get { return Entry; } }
}
}
And no implementation would be complete without a few tests (but tragically, SO won't let me post that much code in one post), so I'll have to leave you to write your tests. But, I left a few of them in so that you could get an idea of how it works:
// http://unlicense.org
using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using mattmc3.Common.Collections.Generic;
namespace mattmc3.Tests.Common.Collections.Generic {
[TestClass]
public class OrderedDictionaryTests {
private OrderedDictionary<string, string> GetAlphabetDictionary(IEqualityComparer<string> comparer = null) {
OrderedDictionary<string, string> alphabet = (comparer == null ? new OrderedDictionary<string, string>() : new OrderedDictionary<string, string>(comparer));
for (var a = Convert.ToInt32('a'); a <= Convert.ToInt32('z'); a++) {
var c = Convert.ToChar(a);
alphabet.Add(c.ToString(), c.ToString().ToUpper());
}
Assert.AreEqual(26, alphabet.Count);
return alphabet;
}
private List<KeyValuePair<string, string>> GetAlphabetList() {
var alphabet = new List<KeyValuePair<string, string>>();
for (var a = Convert.ToInt32('a'); a <= Convert.ToInt32('z'); a++) {
var c = Convert.ToChar(a);
alphabet.Add(new KeyValuePair<string, string>(c.ToString(), c.ToString().ToUpper()));
}
Assert.AreEqual(26, alphabet.Count);
return alphabet;
}
[TestMethod]
public void TestAdd() {
var od = new OrderedDictionary<string, string>();
Assert.AreEqual(0, od.Count);
Assert.AreEqual(-1, od.IndexOf("foo"));
od.Add("foo", "bar");
Assert.AreEqual(1, od.Count);
Assert.AreEqual(0, od.IndexOf("foo"));
Assert.AreEqual(od[0], "bar");
Assert.AreEqual(od["foo"], "bar");
Assert.AreEqual(od.GetItem(0).Key, "foo");
Assert.AreEqual(od.GetItem(0).Value, "bar");
}
[TestMethod]
public void TestRemove() {
var od = new OrderedDictionary<string, string>();
od.Add("foo", "bar");
Assert.AreEqual(1, od.Count);
od.Remove("foo");
Assert.AreEqual(0, od.Count);
}
[TestMethod]
public void TestRemoveAt() {
var od = new OrderedDictionary<string, string>();
od.Add("foo", "bar");
Assert.AreEqual(1, od.Count);
od.RemoveAt(0);
Assert.AreEqual(0, od.Count);
}
[TestMethod]
public void TestClear() {
var od = GetAlphabetDictionary();
Assert.AreEqual(26, od.Count);
od.Clear();
Assert.AreEqual(0, od.Count);
}
[TestMethod]
public void TestOrderIsPreserved() {
var alphabetDict = GetAlphabetDictionary();
var alphabetList = GetAlphabetList();
Assert.AreEqual(26, alphabetDict.Count);
Assert.AreEqual(26, alphabetList.Count);
var keys = alphabetDict.Keys.ToList();
var values = alphabetDict.Values.ToList();
for (var i = 0; i < 26; i++) {
var dictItem = alphabetDict.GetItem(i);
var listItem = alphabetList[i];
var key = keys[i];
var value = values[i];
Assert.AreEqual(dictItem, listItem);
Assert.AreEqual(key, listItem.Key);
Assert.AreEqual(value, listItem.Value);
}
}
[TestMethod]
public void TestTryGetValue() {
var alphabetDict = GetAlphabetDictionary();
string result = null;
Assert.IsFalse(alphabetDict.TryGetValue("abc", out result));
Assert.IsNull(result);
Assert.IsTrue(alphabetDict.TryGetValue("z", out result));
Assert.AreEqual("Z", result);
}
[TestMethod]
public void TestEnumerator() {
var alphabetDict = GetAlphabetDictionary();
var keys = alphabetDict.Keys.ToList();
Assert.AreEqual(26, keys.Count);
var i = 0;
foreach (var kvp in alphabetDict) {
var value = alphabetDict[kvp.Key];
Assert.AreEqual(kvp.Value, value);
i++;
}
}
[TestMethod]
public void TestInvalidIndex() {
var alphabetDict = GetAlphabetDictionary();
try {
var notGonnaWork = alphabetDict[100];
Assert.IsTrue(false, "Exception should have thrown");
}
catch (Exception ex) {
Assert.IsTrue(ex.Message.Contains("index is outside the bounds"));
}
}
[TestMethod]
public void TestMissingKey() {
var alphabetDict = GetAlphabetDictionary();
try {
var notGonnaWork = alphabetDict["abc"];
Assert.IsTrue(false, "Exception should have thrown");
}
catch (Exception ex) {
Assert.IsTrue(ex.Message.Contains("key is not present"));
}
}
[TestMethod]
public void TestUpdateExistingValue() {
var alphabetDict = GetAlphabetDictionary();
Assert.IsTrue(alphabetDict.ContainsKey("c"));
Assert.AreEqual(2, alphabetDict.IndexOf("c"));
Assert.AreEqual(alphabetDict[2], "C");
alphabetDict[2] = "CCC";
Assert.IsTrue(alphabetDict.ContainsKey("c"));
Assert.AreEqual(2, alphabetDict.IndexOf("c"));
Assert.AreEqual(alphabetDict[2], "CCC");
}
[TestMethod]
public void TestInsertValue() {
var alphabetDict = GetAlphabetDictionary();
Assert.IsTrue(alphabetDict.ContainsKey("c"));
Assert.AreEqual(2, alphabetDict.IndexOf("c"));
Assert.AreEqual(alphabetDict[2], "C");
Assert.AreEqual(26, alphabetDict.Count);
Assert.IsFalse(alphabetDict.ContainsValue("ABC"));
alphabetDict.Insert(2, "abc", "ABC");
Assert.IsTrue(alphabetDict.ContainsKey("c"));
Assert.AreEqual(2, alphabetDict.IndexOf("abc"));
Assert.AreEqual(alphabetDict[2], "ABC");
Assert.AreEqual(27, alphabetDict.Count);
Assert.IsTrue(alphabetDict.ContainsValue("ABC"));
}
[TestMethod]
public void TestValueComparer() {
var alphabetDict = GetAlphabetDictionary();
Assert.IsFalse(alphabetDict.ContainsValue("a"));
Assert.IsTrue(alphabetDict.ContainsValue("a", StringComparer.OrdinalIgnoreCase));
}
[TestMethod]
public void TestSortByKeys() {
var alphabetDict = GetAlphabetDictionary();
var reverseAlphabetDict = GetAlphabetDictionary();
Comparison<string> stringReverse = ((x, y) => (String.Equals(x, y) ? 0 : String.Compare(x, y) >= 1 ? -1 : 1));
reverseAlphabetDict.SortKeys(stringReverse);
for (int j = 0, k = 25; j < alphabetDict.Count; j++, k--) {
var ascValue = alphabetDict.GetItem(j);
var dscValue = reverseAlphabetDict.GetItem(k);
Assert.AreEqual(ascValue.Key, dscValue.Key);
Assert.AreEqual(ascValue.Value, dscValue.Value);
}
}
-- UPDATE --
Source for this and other really useful missing core .NET libraries here: https://github.com/mattmc3/dotmore/blob/master/dotmore/Collections/Generic/OrderedDictionary.cs

You're right. There's no generic equivalent of OrderedDictionary in the framework itself.
(That's still the case for .NET 4 too, as far as I'm aware.)

For the record, there is a generic KeyedCollection that allows objects to be indexed by an int and a key. The key must be embedded in the value.

Here's a bizarre find: the System.Web.Util namespace in System.Web.Extensions.dll contains a generic OrderedDictionary<TKey,TValue>
// Type: System.Web.Util.OrderedDictionary`2
// Assembly: System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
// Assembly location: C:\Windows\Microsoft.NET\Framework\v4.0.30319\System.Web.Extensions.dll
namespace System.Web.Util
{
internal class OrderedDictionary<TKey, TValue> : IDictionary<TKey, TValue>, ICollection<KeyValuePair<TKey, TValue>>, IEnumerable<KeyValuePair<TKey, TValue>>, IEnumerable
Not sure why MS placed it there instead of the System.Collections.Generic package, but I assume you can simply copy paste the code and use it (it's internal, so can't use it directly). Looks like the implementation uses a standard dictionary and separate Key/Value lists. Pretty straightforward...
Source code: https://referencesource.microsoft.com/#System.Web.Extensions/Util/OrderedDictionary.cs
A different implementation in System.Runtime.Collections that wraps the non-generic System.Collections.Specialized.OrderedDictionary: https://referencesource.microsoft.com/#System.ServiceModel.Internals/System/Runtime/Collections/OrderedDictionary.cs

For what it's worth, here is how I solved it:
public class PairList<TKey, TValue> : List<KeyValuePair<TKey, TValue>> {
Dictionary<TKey, int> itsIndex = new Dictionary<TKey, int>();
public void Add(TKey key, TValue value) {
Add(new KeyValuePair<TKey, TValue>(key, value));
itsIndex.Add(key, Count-1);
}
public TValue Get(TKey key) {
var idx = itsIndex[key];
return this[idx].Value;
}
}
It can be initialized like this:
var pairList = new PairList<string, string>
{
{ "pitcher", "Ken" },
{ "catcher", "Brad"},
{ "left fielder", "Stan"},
};
and accessed like this:
foreach (var pair in pairList)
{
Console.WriteLine("position: {0}, player: {1}",
pair.Key, pair.Value);
}
// Guaranteed to print in the order of initialization

A major conceptual problem with a generic version of OrderedDictionary is that users of a OrderedDictionary<TKey,TValue> would expect expect to be able to index it either numerically using an int, or by lookup using a TKey. When the only type of key was Object, as was the case with non-generic OrderedDictionary, the type of argument passed to the indexer would be sufficient to distinguish whether what type of indexing operation should be performed. As it is, though, it's unclear how the indexer of an OrderedDictionary<int, TValue> should behave.
If classes like Drawing.Point had recommended and followed a rule that piecewise-mutable structures should expose their mutable elements as fields rather than properties, and refrain from using property setters that modify this, then an OrderedDictionary<TKey,TValue> could efficiently expose a ByIndex property that returned an Indexer struct which held a reference to the dictionary, and had an indexed property whose getter and setter would call GetByIndex and SetByIndex upon it. Thus, one could say something like MyDict.ByIndex[5] += 3; to add 3 to the sixth element of the dictionary.
Unfortunately, for the compiler to accept such a thing, it would be necessary to make the ByIndex property return a new class instance rather than a struct every time it's invoked, eliminating the advantages one would get by avoiding boxing.
In VB.NET, one could get around that issue by using a named indexed property (so MyDict.ByIndex[int] would be a member of MyDict, rather than requiring MyDict.ByIndex to be a member of MyDict which includes an indexer), but C# doesn't allow such things.
It might still have been worthwhile to offer an OrderedDictionary<TKey,TValue> where TKey:class, but much of the reason for providing generics in the first place was to allow their use with value types.

For a lot of purposes I've found one can get by with a List<KeyValuePair<K, V>>. (Not if you need it to extend Dictionary, obviously, and not if you need better than O(n) key-value lookup.)

Right, it's an unfortunate omission. I miss Python's OrderedDict
A dictionary that remembers the order that keys were first inserted. If a new entry overwrites an existing entry, the original insertion position is left unchanged. Deleting an entry and reinserting it will move it to the end.
So I wrote my own OrderedDictionary<K,V> class in C#. How does it work? It maintains two collections - a vanilla unordered dictionary and an ordered list of keys. With this solution, the standard dictionary operations keep their fast complexities, and look up by index is fast too.
https://gist.github.com/hickford/5137384
Here's the interface
/// <summary>
/// A dictionary that remembers the order that keys were first inserted. If a new entry overwrites an existing entry, the original insertion position is left unchanged. Deleting an entry and reinserting it will move it to the end.
/// </summary>
/// <typeparam name="TKey">The type of keys</typeparam>
/// <typeparam name="TValue">The type of values</typeparam>
public interface IOrderedDictionary<TKey, TValue> : IDictionary<TKey, TValue>
{
/// <summary>
/// The value of the element at the given index.
/// </summary>
TValue this[int index] { get; set; }
/// <summary>
/// Find the position of an element by key. Returns -1 if the dictionary does not contain an element with the given key.
/// </summary>
int IndexOf(TKey key);
/// <summary>
/// Insert an element at the given index.
/// </summary>
void Insert(int index, TKey key, TValue value);
/// <summary>
/// Remove the element at the given index.
/// </summary>
void RemoveAt(int index);
}

For those looking for an "official" package option in NuGet, an implementation of a generic OrderedDictionary has been accepted into .NET CoreFX Lab. If all goes well, the type will eventually be approved and integrated to the main .NET CoreFX repo.
There is a possibility that this implementation will be rejected.
The committed implementation can be referenced here
https://github.com/dotnet/corefxlab/blob/57be99a176421992e29009701a99a370983329a6/src/Microsoft.Experimental.Collections/Microsoft/Collections/Extensions/OrderedDictionary.cs
The NuGet package that definitively has this type available for use can be found here
https://www.nuget.org/packages/Microsoft.Experimental.Collections/1.0.6-e190117-3
Or you can install the package within Visual Studio. Browse for the package "Microsoft.Experimental.Collections" and make sure the "Include prerelease" checkbox is selected.
Will update this post if and when the type is made officially available.

There is SortedDictionary<TKey, TValue>. Although semantically close, I am not claiming it's the same as OrderedDictionary simply because they are not. Even from performance characteristics. However the very interesting and quite important difference between Dictionary<TKey, TValue> (and to that extent OrderedDictionary and implementations provided in answers) and SortedDictionary is that the latter is using binary tree underneath. This is critical distinction because it makes the class immune to memory constraints applied to generic class. See this thread about OutOfMemoryExceptions thrown when generic class is used for handling large set of key-value pairs.
How to figure out the max value for capacity parameter passed to Dictionary constructor to avoid OutOfMemoryException?

As a follow up to the comment from #V.B. here's an accessible implementation of the System.Runtime.Collections.OrderedDictionary<,>. I was originally going to access it by reflection and provide it via a factory but the dll this is in does not seem to be very accessible at all so I just pulled the source itself.
One thing to note is the indexer here will not throw KeyNotFoundException. I absolutely hate that convention and that was the 1 liberty i took in this implementation. If that's important to you, just replace the line for return default(TValue);. Uses C# 6 (compatible with Visual Studio 2013)
/// <summary>
/// System.Collections.Specialized.OrderedDictionary is NOT generic.
/// This class is essentially a generic wrapper for OrderedDictionary.
/// </summary>
/// <remarks>
/// Indexer here will NOT throw KeyNotFoundException
/// </remarks>
public class OrderedDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IDictionary
{
private readonly OrderedDictionary _privateDictionary;
public OrderedDictionary()
{
_privateDictionary = new OrderedDictionary();
}
public OrderedDictionary(IDictionary<TKey, TValue> dictionary)
{
if (dictionary == null) return;
_privateDictionary = new OrderedDictionary();
foreach (var pair in dictionary)
{
_privateDictionary.Add(pair.Key, pair.Value);
}
}
public bool IsReadOnly => false;
public int Count => _privateDictionary.Count;
int ICollection.Count => _privateDictionary.Count;
object ICollection.SyncRoot => ((ICollection)_privateDictionary).SyncRoot;
bool ICollection.IsSynchronized => ((ICollection)_privateDictionary).IsSynchronized;
bool IDictionary.IsFixedSize => ((IDictionary)_privateDictionary).IsFixedSize;
bool IDictionary.IsReadOnly => _privateDictionary.IsReadOnly;
ICollection IDictionary.Keys => _privateDictionary.Keys;
ICollection IDictionary.Values => _privateDictionary.Values;
void IDictionary.Add(object key, object value)
{
_privateDictionary.Add(key, value);
}
void IDictionary.Clear()
{
_privateDictionary.Clear();
}
bool IDictionary.Contains(object key)
{
return _privateDictionary.Contains(key);
}
IDictionaryEnumerator IDictionary.GetEnumerator()
{
return _privateDictionary.GetEnumerator();
}
void IDictionary.Remove(object key)
{
_privateDictionary.Remove(key);
}
object IDictionary.this[object key]
{
get { return _privateDictionary[key]; }
set { _privateDictionary[key] = value; }
}
void ICollection.CopyTo(Array array, int index)
{
_privateDictionary.CopyTo(array, index);
}
public TValue this[TKey key]
{
get
{
if (key == null) throw new ArgumentNullException(nameof(key));
if (_privateDictionary.Contains(key))
{
return (TValue) _privateDictionary[key];
}
return default(TValue);
}
set
{
if (key == null) throw new ArgumentNullException(nameof(key));
_privateDictionary[key] = value;
}
}
public ICollection<TKey> Keys
{
get
{
var keys = new List<TKey>(_privateDictionary.Count);
keys.AddRange(_privateDictionary.Keys.Cast<TKey>());
return keys.AsReadOnly();
}
}
public ICollection<TValue> Values
{
get
{
var values = new List<TValue>(_privateDictionary.Count);
values.AddRange(_privateDictionary.Values.Cast<TValue>());
return values.AsReadOnly();
}
}
public void Add(KeyValuePair<TKey, TValue> item)
{
Add(item.Key, item.Value);
}
public void Add(TKey key, TValue value)
{
if (key == null) throw new ArgumentNullException(nameof(key));
_privateDictionary.Add(key, value);
}
public void Clear()
{
_privateDictionary.Clear();
}
public bool Contains(KeyValuePair<TKey, TValue> item)
{
if (item.Key == null || !_privateDictionary.Contains(item.Key))
{
return false;
}
return _privateDictionary[item.Key].Equals(item.Value);
}
public bool ContainsKey(TKey key)
{
if (key == null) throw new ArgumentNullException(nameof(key));
return _privateDictionary.Contains(key);
}
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
{
if (array == null) throw new ArgumentNullException(nameof(array));
if (arrayIndex < 0) throw new ArgumentOutOfRangeException(nameof(arrayIndex));
if (array.Rank > 1 || arrayIndex >= array.Length
|| array.Length - arrayIndex < _privateDictionary.Count)
throw new ArgumentException("Bad Copy ToArray", nameof(array));
var index = arrayIndex;
foreach (DictionaryEntry entry in _privateDictionary)
{
array[index] =
new KeyValuePair<TKey, TValue>((TKey) entry.Key, (TValue) entry.Value);
index++;
}
}
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
{
foreach (DictionaryEntry entry in _privateDictionary)
{
yield return
new KeyValuePair<TKey, TValue>((TKey) entry.Key, (TValue) entry.Value);
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public bool Remove(KeyValuePair<TKey, TValue> item)
{
if (false == Contains(item)) return false;
_privateDictionary.Remove(item.Key);
return true;
}
public bool Remove(TKey key)
{
if (key == null) throw new ArgumentNullException(nameof(key));
if (false == _privateDictionary.Contains(key)) return false;
_privateDictionary.Remove(key);
return true;
}
public bool TryGetValue(TKey key, out TValue value)
{
if (key == null) throw new ArgumentNullException(nameof(key));
var keyExists = _privateDictionary.Contains(key);
value = keyExists ? (TValue) _privateDictionary[key] : default(TValue);
return keyExists;
}
}
Pull requests/discussion accepted on GitHub

I implemented a generic OrderedDictionary<TKey, TValue> by wraping around SortedList<TKey, TValue> and adding a private Dictionary<TKey, int> _order. Then I created an internal implementation of Comparer<TKey>, passing a reference to the _order dictionary. Then I use this comparer for the internal SortedList. This class keeps the order of elements passed to the constructor and order of additions.
This implementation has almost the same big O characteristics as SortedList<TKey, TValue> since adding and removing to _order is O(1). Each element will take (according to the book 'C# 4 in a Nutshell', p. 292, table 7-1) additional memory space of 22 (overhead) + 4 (int order) + TKey size (let's assume 8) = 34. Together with SortedList<TKey, TValue>'s overhead of two bytes, the total overhead is 36 bytes, while the same book says that non-generic OrderedDictionary has an overhead of 59 bytes.
If I pass sorted=true to constructor, then _order is not used at all, the OrderedDictionary<TKey, TValue> is exactly SortedList<TKey, TValue> with minor overhead for wrapping, if at all meaningful.
I am going to store not-so-many large reference objects in the OrderedDictionary<TKey, TValue>, so for me this ca. 36 bytes overhead is tolerable.
The main code is below. The complete updated code is on this gist.
public class OrderedList<TKey, TValue> : IDictionary<TKey, TValue>, IDictionary
{
private readonly Dictionary<TKey, int> _order;
private readonly SortedList<TKey, TValue> _internalList;
private readonly bool _sorted;
private readonly OrderComparer _comparer;
public OrderedList(IDictionary<TKey, TValue> dictionary, bool sorted = false)
{
_sorted = sorted;
if (dictionary == null)
dictionary = new Dictionary<TKey, TValue>();
if (_sorted)
{
_internalList = new SortedList<TKey, TValue>(dictionary);
}
else
{
_order = new Dictionary<TKey, int>();
_comparer = new OrderComparer(ref _order);
_internalList = new SortedList<TKey, TValue>(_comparer);
// Keep order of the IDictionary
foreach (var kvp in dictionary)
{
Add(kvp);
}
}
}
public OrderedList(bool sorted = false)
: this(null, sorted)
{
}
private class OrderComparer : Comparer<TKey>
{
public Dictionary<TKey, int> Order { get; set; }
public OrderComparer(ref Dictionary<TKey, int> order)
{
Order = order;
}
public override int Compare(TKey x, TKey y)
{
var xo = Order[x];
var yo = Order[y];
return xo.CompareTo(yo);
}
}
private void ReOrder()
{
var i = 0;
_order = _order.OrderBy(kvp => kvp.Value).ToDictionary(kvp => kvp.Key, kvp => i++);
_comparer.Order = _order;
_lastOrder = _order.Values.Max() + 1;
}
public void Add(TKey key, TValue value)
{
if (!_sorted)
{
_order.Add(key, _lastOrder);
_lastOrder++;
// Very rare event
if (_lastOrder == int.MaxValue)
ReOrder();
}
_internalList.Add(key, value);
}
public bool Remove(TKey key)
{
var result = _internalList.Remove(key);
if (!_sorted)
_order.Remove(key);
return result;
}
// Other IDictionary<> + IDictionary members implementation wrapping around _internalList
// ...
}

This is not yet another version/solution of an OrderedDictionary<,> but an experiment I did testing each of 4 versions mentioned in the answers: of #Colonel Panic, #mattmc3, #V.B. #Chris Marisic. It is meant as a feedback. Well, partial because I have to admit I haven't dissected the code, so there may be differences in functionality or safety checks. But still, I thought feedback would be useful on their performance. And as you'll see time can get from a couple of milliseconds to a quarter of hour.
Then I scribbled a naive minimal version with 2 lists of key and value class objects with O(n) search just to see the magnitude of the benefit of O(1) access.
Testbed is Microsoft Visual Studio Community 2019 with Unity 3D, 4 consecutive times for each test and the code that I wanted to replicate a real-ish scenario in is
using System.Text;
using UnityEngine;
public class TessyOne : MonoBehaviour
{
public const int iterations = 50000;
private System.Diagnostics.Stopwatch stopwatch;
private System.Random random;
public float stopwatchDuration;
public class Ala
{
public int inta;
public float fla;
public string stra;
public Ben bena;
public Ala(int i, float f, string s, Ben b)
{
inta = i; fla = f; stra = s; bena = b;
}
}
public class Ben
{
public int inte;
public float fle;
public string stre;
public Ben(int i, float f, string s)
{
inte = i; fle = f; stre = s;
}
}
//public Naive.OrderedDictionary<Ala, Ben> alasToBens = new Naive.OrderedDictionary<Ala, Ben>();
//public Hickford.OrderedDictionary<Ala, Ben> alasToBens = new Hickford.OrderedDictionary<Ala, Ben>();
//public Mattmc3.OrderedDictionary<Ala, Ben> alasToBens = new Mattmc3.OrderedDictionary<Ala, Ben>();
public Marisic.OrderedDictionary<Ala, Ben> alasToBens = new Marisic.OrderedDictionary<Ala, Ben>();
//public VB.OrderedList<Ala, Ben> alasToBens = new VB.OrderedList<Ala, Ben>(null, false);
Ala[] alarray = new Ala[iterations];
Ben[] berray = new Ben[iterations];
// This is the entry point of the application
private void Start()
{
stopwatch = new System.Diagnostics.Stopwatch();
random = new System.Random(2020);
for(int i = 0; i < iterations; ++i)
{
berray[i] = new Ben(random.Next(),
(float)random.NextDouble(),
MakeRandomString((ushort)random.Next(1, 10)));
alarray[i] = new Ala(random.Next(),
(float)random.NextDouble(),
MakeRandomString((ushort)random.Next(1, 10)),
berray[i]);
// uncomment for testing ContainsKey() and Remove(), comment for Add()
alasToBens.Add(alarray[i], berray[i]);
}
stopwatch.Start();
for(int i = iterations - 1; i > -1; --i)
{
//alasToBens.Add(alarray[i], berray[i]);
//alasToBens.ContainsKey(alarray[i]);
alasToBens.Remove(alarray[i]);
}
stopwatch.Stop();
stopwatchDuration = stopwatch.ElapsedMilliseconds;
}
public string MakeRandomString(ushort length)
{
StringBuilder sb = new StringBuilder();
for(ushort u = 0; u < length; ++u)
{
sb.Append((char)Random.Range(33, 126)); // regular ASCII chars
}
return sb.ToString();
}
}
Note that the tests are for worst case scenarios in the case of naive version at least, as it iterates through the collection from index 0 through iterations and searching is done from end to start. I measured Add(), ContainsKey() and Remove() in milliseconds for a dictionary of 50000 entries.
Results:
+----------+----------------+----------------+--------------------------------+
| ms | Add() | ContainsKey() | Remove() |
+----------+----------------+----------------+--------------------------------+
| Hickford | 7, 8, 7, 8 | 2, 2, 3, 2 | 7400, 7503, 7419, 7421 |
| Mattmc3 | 23, 24, 24, 23 | 3, 3, 3, 3 | 890404, 913465, 875387, 877792 |
| Marisic | 27, 28, 28, 27 | 4, 4, 4, 4 | 27401, 27627, 27341, 27349 |
| V.B. | 76, 76, 75, 75 | 59, 60, 60, 60 | 66, 67, 67, 67 |
| | | | |
| Naive | 19651, 19761 | 25335, 25416 | 25259, 25306 |
+----------+----------------+----------------+--------------------------------+

Are there any implementations of multiset for .Net?

I'm looking for a .Net implementation of a multiset. Can anyone recommend a good one?
(A multiset, or bag, is a set that can have duplicate values, and on which you can do set operations: intersection, difference, etc. A shopping cart for instance could be thought of as a multiset because you can have multiple occurrences of the same product.)

I do not know about one, however you could use a Dictionary for that, in which the value is the quantity of the item. And when the item is added for the second time, you vould increase the value for it in the dictionary.
An other possibility would be to simply use a List of items, in which you could put duplicates. This might be a better approach for a shopping cart.

Anything calling itself a C# implementation of a multiset should not be based on a Dictionary internally. Dictionaries are hash tables, unordered collections. C++'s sets, multisets, maps, and multimaps are ordered. Internally each is represented as some flavor of a self-balancing binary search tree.
In C# we should then use a SortedDictionary as the basis of our implementation as according to Microsoft's own documentation a SortedDictionary "is a binary search tree with O(log n) retrieval". A basic multiset can be implemented as follows:
public class SortedMultiSet<T> : IEnumerable<T>
{
private SortedDictionary<T, int> _dict;
public SortedMultiSet()
{
_dict = new SortedDictionary<T, int>();
}
public SortedMultiSet(IEnumerable<T> items) : this()
{
Add(items);
}
public bool Contains(T item)
{
return _dict.ContainsKey(item);
}
public void Add(T item)
{
if (_dict.ContainsKey(item))
_dict[item]++;
else
_dict[item] = 1;
}
public void Add(IEnumerable<T> items)
{
foreach (var item in items)
Add(item);
}
public void Remove(T item)
{
if (!_dict.ContainsKey(item))
throw new ArgumentException();
if (--_dict[item] == 0)
_dict.Remove(item);
}
// Return the last value in the multiset
public T Peek()
{
if (!_dict.Any())
throw new NullReferenceException();
return _dict.Last().Key;
}
// Return the last value in the multiset and remove it.
public T Pop()
{
T item = Peek();
Remove(item);
return item;
}
public IEnumerator<T> GetEnumerator()
{
foreach(var kvp in _dict)
for(int i = 0; i < kvp.Value; i++)
yield return kvp.Key;
}
IEnumerator IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
}

Another option is to just wrap SortedSet, but instead of storing your type T in it, you store the value tuple (T value, int counter) where counter goes up by 1 with each new instance of value that is inserted. Essentially you're forcing the values to be distinct. You can efficiently use GetViewBetween() to find the largest value of counter for a particular value, then increment it to get the counter for a newly-added value. And unlike the count dictionary solution, you can use GetViewBetween() to replicate the functionality equal_range, lower_bound, and upper_bound gives in C++. Here is some code showing what I mean:
public class SortedMultiSet<T> : IEnumerable<T>
{
public void Add(T value)
{
var view = set.GetViewBetween((value, 0), (value, int.MaxValue));
int nextCounter = view.Count > 0 ? view.Max.counter + 1 : 0;
set.Add((value, nextCounter));
}
public bool RemoveOne(T value)
{
var view = set.GetViewBetween((value, 0), (value, int.MaxValue));
if (view.Count == 0) return false;
set.Remove(view.Max);
return true;
}
public bool RemoveAll(T value)
{
var view = set.GetViewBetween((value, 0), (value, int.MaxValue));
bool result = view.Count > 0;
view.Clear();
return result;
}
public SortedMultiSet<T> GetViewBetween(T min, T max)
{
var result = new SortedMultiSet<T>();
result.set = set.GetViewBetween((min, 0), (max, int.MaxValue));
return result;
}
public IEnumerator<T> GetEnumerator() =>
set.Select(x => x.value).GetEnumerator();
IEnumerator IEnumerable.GetEnumerator() =>
set.Select(x => x.value).GetEnumerator();
private SortedSet<(T value, int counter)> set =
new SortedSet<(T value, int counter)>();
}
Now you can write something like this:
var multiset = new SortedMultiSet<int>();
foreach (int i in new int[] { 1, 2, 2, 3, 4, 5, 5, 6, 7, 7, 8 })
{
multiset.Add(i);
}
foreach (int i in multiset.GetViewBetween(2, 7))
{
Console.Write(i + " "); // Output: 2 2 3 4 5 5 6 7 7
}
In the past, there were some issues where GetViewBetween() ran in time O(output size), rather than time O(log n), but I think those have been resolved. At the time it would count up nodes to cache the count, it now uses hierarchical counts to perform Count operations efficiently. See this StackOverflow post and this library code.

public class Multiset<T>: ICollection<T>
{
private readonly Dictionary<T, int> data;
public Multiset()
{
data = new Dictionary<T, int>();
}
private Multiset(Dictionary<T, int> data)
{
this.data = data;
}
public void Add(T item)
{
int count = 0;
data.TryGetValue(item, out count);
count++;
data[item] = count;
}
public void Clear()
{
data.Clear();
}
public Multiset<T> Except(Multiset<T> another)
{
Multiset<T> copy = new Multiset<T>(new Dictionary<T, int>(data));
foreach (KeyValuePair<T, int> kvp in another.data)
{
int count;
if (copy.data.TryGetValue(kvp.Key, out count))
{
if (count > kvp.Value)
{
copy.data[kvp.Key] = count - kvp.Value;
}
else
{
copy.data.Remove(kvp.Key);
}
}
}
return copy;
}
public Multiset<T> Intersection(Multiset<T> another)
{
Dictionary<T, int> newData = new Dictionary<T, int>();
foreach (T t in data.Keys.Intersect(another.data.Keys))
{
newData[t] = Math.Min(data[t], another.data[t]);
}
return new Multiset<T>(newData);
}
public bool Contains(T item)
{
return data.ContainsKey(item);
}
public void CopyTo(T[] array, int arrayIndex)
{
foreach (KeyValuePair<T, int> kvp in data)
{
for (int i = 0; i < kvp.Value; i++)
{
array[arrayIndex] = kvp.Key;
arrayIndex++;
}
}
}
public IEnumerable<T> Mode()
{
if (!data.Any())
{
return Enumerable.Empty<T>();
}
int modalFrequency = data.Values.Max();
return data.Where(kvp => kvp.Value == modalFrequency).Select(kvp => kvp.Key);
}
public int Count
{
get
{
return data.Values.Sum();
}
}
public bool IsReadOnly
{
get
{
return false;
}
}
public bool Remove(T item)
{
int count;
if (!data.TryGetValue(item, out count))
{
return false;
}
count--;
if (count == 0)
{
data.Remove(item);
}
else
{
data[item] = count;
}
return true;
}
public IEnumerator<T> GetEnumerator()
{
return new MultisetEnumerator<T>(this);
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return new MultisetEnumerator<T>(this);
}
private class MultisetEnumerator<T> : IEnumerator<T>
{
public MultisetEnumerator(Multiset<T> multiset)
{
this.multiset = multiset;
baseEnumerator = multiset.data.GetEnumerator();
index = 0;
}
private readonly Multiset<T> multiset;
private readonly IEnumerator<KeyValuePair<T, int>> baseEnumerator;
private int index;
public T Current
{
get
{
return baseEnumerator.Current.Key;
}
}
public void Dispose()
{
baseEnumerator.Dispose();
}
object System.Collections.IEnumerator.Current
{
get
{
return baseEnumerator.Current.Key;
}
}
public bool MoveNext()
{
KeyValuePair<T, int> kvp = baseEnumerator.Current;
if (index < (kvp.Value - 1))
{
index++;
return true;
}
else
{
bool result = baseEnumerator.MoveNext();
index = 0;
return result;
}
}
public void Reset()
{
baseEnumerator.Reset();
}
}
}

You can use this implementation of a sorted multiset: SortedMultiSet.cs

We Keep Coding

C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.

Generic form of NameValueCollection in .Net - c#

Nothing inbuilt; there is Lookup<TKey,TValue> which operates as a multi-map, but that is immutable. I wrote a mutable EditableLookup<TKey,TValue> for MiscUtil which may help.

Related

C# - Dictionary with Behaviour of a Ring List?

Collection that allows only unique items in .NET?

SortList duplicated key, but it shouldn't

Why no generic implementation of OrderedDictionary? [duplicate]

Are there any implementations of multiset for .Net?

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