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generic <typename TKey, typename TValue>
public ref class Dictionary : System::Collections::Generic::ICollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IDictionary<TKey, TValue>, System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IReadOnlyCollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IReadOnlyDictionary<TKey, TValue>, System::Collections::IDictionary
generic <typename TKey, typename TValue>
public ref class Dictionary : System::Collections::Generic::ICollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IDictionary<TKey, TValue>, System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IReadOnlyCollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IReadOnlyDictionary<TKey, TValue>, System::Collections::IDictionary, System::Runtime::Serialization::IDeserializationCallback, System::Runtime::Serialization::ISerializable
generic <typename TKey, typename TValue>
public ref class Dictionary : System::Collections::Generic::ICollection<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::Generic::IDictionary<TKey, TValue>, System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>>, System::Collections::IDictionary, System::Runtime::Serialization::IDeserializationCallback, System::Runtime::Serialization::ISerializable
public class Dictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyDictionary<TKey,TValue>, System.Collections.IDictionary
public class Dictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyDictionary<TKey,TValue>, System.Collections.IDictionary, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable
[System.Runtime.InteropServices.ComVisible(false)]
[System.Serializable]
public class Dictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.IDictionary, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable
[System.Runtime.InteropServices.ComVisible(false)]
[System.Serializable]
public class Dictionary<TKey,TValue> : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IDictionary<TKey,TValue>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<TKey,TValue>>, System.Collections.Generic.IReadOnlyDictionary<TKey,TValue>, System.Collections.IDictionary, System.Runtime.Serialization.IDeserializationCallback, System.Runtime.Serialization.ISerializable
type Dictionary<'Key, 'Value> = class
    interface ICollection<KeyValuePair<'Key, 'Value>>
    interface seq<KeyValuePair<'Key, 'Value>>
    interface IEnumerable
    interface IDictionary<'Key, 'Value>
    interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>
    interface IReadOnlyDictionary<'Key, 'Value>
    interface ICollection
    interface IDictionary
type Dictionary<'Key, 'Value> = class
    interface ICollection<KeyValuePair<'Key, 'Value>>
    interface seq<KeyValuePair<'Key, 'Value>>
    interface IEnumerable
    interface IDictionary<'Key, 'Value>
    interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>
    interface IReadOnlyDictionary<'Key, 'Value>
    interface ICollection
    interface IDictionary
    interface IDeserializationCallback
    interface ISerializable
[<System.Runtime.InteropServices.ComVisible(false)>]
[<System.Serializable>]
type Dictionary<'Key, 'Value> = class
    interface IDictionary<'Key, 'Value>
    interface ICollection<KeyValuePair<'Key, 'Value>>
    interface seq<KeyValuePair<'Key, 'Value>>
    interface IDictionary
    interface ICollection
    interface IEnumerable
    interface ISerializable
    interface IDeserializationCallback
[<System.Runtime.InteropServices.ComVisible(false)>]
[<System.Serializable>]
type Dictionary<'Key, 'Value> = class
    interface IDictionary<'Key, 'Value>
    interface ICollection<KeyValuePair<'Key, 'Value>>
    interface IDictionary
    interface ICollection
    interface IReadOnlyDictionary<'Key, 'Value>
    interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>
    interface seq<KeyValuePair<'Key, 'Value>>
    interface IEnumerable
    interface ISerializable
    interface IDeserializationCallback
[<System.Runtime.InteropServices.ComVisible(false)>]
[<System.Serializable>]
type Dictionary<'Key, 'Value> = class
    interface IDictionary<'Key, 'Value>
    interface ICollection<KeyValuePair<'Key, 'Value>>
    interface seq<KeyValuePair<'Key, 'Value>>
    interface IEnumerable
    interface IDictionary
    interface ICollection
    interface IReadOnlyDictionary<'Key, 'Value>
    interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>
    interface ISerializable
    interface IDeserializationCallback
type Dictionary<'Key, 'Value> = class
    interface IDictionary<'Key, 'Value>
    interface ICollection<KeyValuePair<'Key, 'Value>>
    interface IReadOnlyDictionary<'Key, 'Value>
    interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>
    interface seq<KeyValuePair<'Key, 'Value>>
    interface IDictionary
    interface ICollection
    interface IEnumerable
[<System.Runtime.InteropServices.ComVisible(false)>]
[<System.Serializable>]
type Dictionary<'Key, 'Value> = class
    interface IDictionary<'Key, 'Value>
    interface IDictionary
    interface IReadOnlyDictionary<'Key, 'Value>
    interface ISerializable
    interface IDeserializationCallback
    interface ICollection<KeyValuePair<'Key, 'Value>>
    interface seq<KeyValuePair<'Key, 'Value>>
    interface IEnumerable
    interface ICollection
    interface IReadOnlyCollection<KeyValuePair<'Key, 'Value>>
Public Class Dictionary(Of TKey, TValue)
Implements ICollection(Of KeyValuePair(Of TKey, TValue)), IDictionary, IDictionary(Of TKey, TValue), IEnumerable(Of KeyValuePair(Of TKey, TValue)), IReadOnlyCollection(Of KeyValuePair(Of TKey, TValue)), IReadOnlyDictionary(Of TKey, TValue)
Public Class Dictionary(Of TKey, TValue)
Implements ICollection(Of KeyValuePair(Of TKey, TValue)), IDeserializationCallback, IDictionary, IDictionary(Of TKey, TValue), IEnumerable(Of KeyValuePair(Of TKey, TValue)), IReadOnlyCollection(Of KeyValuePair(Of TKey, TValue)), IReadOnlyDictionary(Of TKey, TValue), ISerializable
Public Class Dictionary(Of TKey, TValue)
Implements ICollection(Of KeyValuePair(Of TKey, TValue)), IDeserializationCallback, IDictionary, IDictionary(Of TKey, TValue), IEnumerable(Of KeyValuePair(Of TKey, TValue)), ISerializable

Type Parameters

Examples

The following code example creates an empty Dictionary<TKey,TValue> of strings with string keys and uses the Add method to add some elements. The example demonstrates that the Add method throws an ArgumentException when attempting to add a duplicate key.

The example uses the Item[] property (the indexer in C#) to retrieve values, demonstrating that a KeyNotFoundException is thrown when a requested key is not present, and showing that the value associated with a key can be replaced.

The example shows how to use the TryGetValue method as a more efficient way to retrieve values if a program often must try key values that are not in the dictionary, and it shows how to use the ContainsKey method to test whether a key exists before calling the Add method.

The example shows how to enumerate the keys and values in the dictionary and how to enumerate the keys and values alone using the Keys property and the Values property.

Finally, the example demonstrates the Remove method.

using namespace System; using namespace System::Collections::Generic; public ref class Example public: static void Main() // Create a new dictionary of strings, with string keys. Dictionary<String^, String^>^ openWith = gcnew Dictionary<String^, String^>(); // Add some elements to the dictionary. There are no // duplicate keys, but some of the values are duplicates. openWith->Add("txt", "notepad.exe"); openWith->Add("bmp", "paint.exe"); openWith->Add("dib", "paint.exe"); openWith->Add("rtf", "wordpad.exe"); // The Add method throws an exception if the new key is // already in the dictionary. openWith->Add("txt", "winword.exe"); catch (ArgumentException^) Console::WriteLine("An element with Key = \"txt\" already exists."); // The Item property is another name for the indexer, so you // can omit its name when accessing elements. Console::WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]); // The indexer can be used to change the value associated // with a key. openWith["rtf"] = "winword.exe"; Console::WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]); // If a key does not exist, setting the indexer for that key // adds a new key/value pair. openWith["doc"] = "winword.exe"; // The indexer throws an exception if the requested key is // not in the dictionary. Console::WriteLine("For key = \"tif\", value = {0}.", openWith["tif"]); catch (KeyNotFoundException^) Console::WriteLine("Key = \"tif\" is not found."); // When a program often has to try keys that turn out not to // be in the dictionary, TryGetValue can be a more efficient // way to retrieve values. String^ value = ""; if (openWith->TryGetValue("tif", value)) Console::WriteLine("For key = \"tif\", value = {0}.", value); Console::WriteLine("Key = \"tif\" is not found."); // ContainsKey can be used to test keys before inserting // them. if (!openWith->ContainsKey("ht")) openWith->Add("ht", "hypertrm.exe"); Console::WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]); // When you use foreach to enumerate dictionary elements, // the elements are retrieved as KeyValuePair objects. Console::WriteLine(); for each( KeyValuePair<String^, String^> kvp in openWith ) Console::WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value); // To get the values alone, use the Values property. Dictionary<String^, String^>::ValueCollection^ valueColl = openWith->Values; // The elements of the ValueCollection are strongly typed // with the type that was specified for dictionary values. Console::WriteLine(); for each( String^ s in valueColl ) Console::WriteLine("Value = {0}", s); // To get the keys alone, use the Keys property. Dictionary<String^, String^>::KeyCollection^ keyColl = openWith->Keys; // The elements of the KeyCollection are strongly typed // with the type that was specified for dictionary keys. Console::WriteLine(); for each( String^ s in keyColl ) Console::WriteLine("Key = {0}", s); // Use the Remove method to remove a key/value pair. Console::WriteLine("\nRemove(\"doc\")"); openWith->Remove("doc"); if (!openWith->ContainsKey("doc")) Console::WriteLine("Key \"doc\" is not found."); int main() Example::Main(); /* This code example produces the following output: An element with Key = "txt" already exists. For key = "rtf", value = wordpad.exe. For key = "rtf", value = winword.exe. Key = "tif" is not found. Key = "tif" is not found. Value added for key = "ht": hypertrm.exe Key = txt, Value = notepad.exe Key = bmp, Value = paint.exe Key = dib, Value = paint.exe Key = rtf, Value = winword.exe Key = doc, Value = winword.exe Key = ht, Value = hypertrm.exe Value = notepad.exe Value = paint.exe Value = paint.exe Value = winword.exe Value = winword.exe Value = hypertrm.exe Key = txt Key = bmp Key = dib Key = rtf Key = doc Key = ht Remove("doc") Key "doc" is not found. // Create a new dictionary of strings, with string keys. Dictionary<string, string> openWith = new Dictionary<string, string>(); // Add some elements to the dictionary. There are no // duplicate keys, but some of the values are duplicates. openWith.Add("txt", "notepad.exe"); openWith.Add("bmp", "paint.exe"); openWith.Add("dib", "paint.exe"); openWith.Add("rtf", "wordpad.exe"); // The Add method throws an exception if the new key is // already in the dictionary. openWith.Add("txt", "winword.exe"); catch (ArgumentException) Console.WriteLine("An element with Key = \"txt\" already exists."); // The Item property is another name for the indexer, so you // can omit its name when accessing elements. Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]); // The indexer can be used to change the value associated // with a key. openWith["rtf"] = "winword.exe"; Console.WriteLine("For key = \"rtf\", value = {0}.", openWith["rtf"]); // If a key does not exist, setting the indexer for that key // adds a new key/value pair. openWith["doc"] = "winword.exe"; // The indexer throws an exception if the requested key is // not in the dictionary. Console.WriteLine("For key = \"tif\", value = {0}.", openWith["tif"]); catch (KeyNotFoundException) Console.WriteLine("Key = \"tif\" is not found."); // When a program often has to try keys that turn out not to // be in the dictionary, TryGetValue can be a more efficient // way to retrieve values. string value = ""; if (openWith.TryGetValue("tif", out value)) Console.WriteLine("For key = \"tif\", value = {0}.", value); Console.WriteLine("Key = \"tif\" is not found."); // ContainsKey can be used to test keys before inserting // them. if (!openWith.ContainsKey("ht")) openWith.Add("ht", "hypertrm.exe"); Console.WriteLine("Value added for key = \"ht\": {0}", openWith["ht"]); // When you use foreach to enumerate dictionary elements, // the elements are retrieved as KeyValuePair objects. Console.WriteLine(); foreach( KeyValuePair<string, string> kvp in openWith ) Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value); // To get the values alone, use the Values property. Dictionary<string, string>.ValueCollection valueColl = openWith.Values; // The elements of the ValueCollection are strongly typed // with the type that was specified for dictionary values. Console.WriteLine(); foreach( string s in valueColl ) Console.WriteLine("Value = {0}", s); // To get the keys alone, use the Keys property. Dictionary<string, string>.KeyCollection keyColl = openWith.Keys; // The elements of the KeyCollection are strongly typed // with the type that was specified for dictionary keys. Console.WriteLine(); foreach( string s in keyColl ) Console.WriteLine("Key = {0}", s); // Use the Remove method to remove a key/value pair. Console.WriteLine("\nRemove(\"doc\")"); openWith.Remove("doc"); if (!openWith.ContainsKey("doc")) Console.WriteLine("Key \"doc\" is not found."); /* This code example produces the following output: An element with Key = "txt" already exists. For key = "rtf", value = wordpad.exe. For key = "rtf", value = winword.exe. Key = "tif" is not found. Key = "tif" is not found. Value added for key = "ht": hypertrm.exe Key = txt, Value = notepad.exe Key = bmp, Value = paint.exe Key = dib, Value = paint.exe Key = rtf, Value = winword.exe Key = doc, Value = winword.exe Key = ht, Value = hypertrm.exe Value = notepad.exe Value = paint.exe Value = paint.exe Value = winword.exe Value = winword.exe Value = hypertrm.exe Key = txt Key = bmp Key = dib Key = rtf Key = doc Key = ht Remove("doc") Key "doc" is not found. Imports System.Collections.Generic Public Class Example Public Shared Sub Main() ' Create a new dictionary of strings, with string keys. Dim openWith As New Dictionary(Of String, String) ' Add some elements to the dictionary. There are no ' duplicate keys, but some of the values are duplicates. openWith.Add("txt", "notepad.exe") openWith.Add("bmp", "paint.exe") openWith.Add("dib", "paint.exe") openWith.Add("rtf", "wordpad.exe") ' The Add method throws an exception if the new key is ' already in the dictionary. openWith.Add("txt", "winword.exe") Catch Console.WriteLine("An element with Key = ""txt"" already exists.") End Try ' The Item property is the default property, so you ' can omit its name when accessing elements. Console.WriteLine("For key = ""rtf"", value = {0}.", _ openWith("rtf")) ' The default Item property can be used to change the value ' associated with a key. openWith("rtf") = "winword.exe" Console.WriteLine("For key = ""rtf"", value = {0}.", _ openWith("rtf")) ' If a key does not exist, setting the default Item property ' for that key adds a new key/value pair. openWith("doc") = "winword.exe" ' The default Item property throws an exception if the requested ' key is not in the dictionary. Console.WriteLine("For key = ""tif"", value = {0}.", _ openWith("tif")) Catch Console.WriteLine("Key = ""tif"" is not found.") End Try ' When a program often has to try keys that turn out not to ' be in the dictionary, TryGetValue can be a more efficient ' way to retrieve values. Dim value As String = "" If openWith.TryGetValue("tif", value) Then Console.WriteLine("For key = ""tif"", value = {0}.", value) Console.WriteLine("Key = ""tif"" is not found.") End If ' ContainsKey can be used to test keys before inserting ' them. If Not openWith.ContainsKey("ht") Then openWith.Add("ht", "hypertrm.exe") Console.WriteLine("Value added for key = ""ht"": {0}", _ openWith("ht")) End If ' When you use foreach to enumerate dictionary elements, ' the elements are retrieved as KeyValuePair objects. Console.WriteLine() For Each kvp As KeyValuePair(Of String, String) In openWith Console.WriteLine("Key = {0}, Value = {1}", _ kvp.Key, kvp.Value) Next kvp ' To get the values alone, use the Values property. Dim valueColl As _ Dictionary(Of String, String).ValueCollection = _ openWith.Values ' The elements of the ValueCollection are strongly typed ' with the type that was specified for dictionary values. Console.WriteLine() For Each s As String In valueColl Console.WriteLine("Value = {0}", s) Next s ' To get the keys alone, use the Keys property. Dim keyColl As _ Dictionary(Of String, String).KeyCollection = _ openWith.Keys ' The elements of the KeyCollection are strongly typed ' with the type that was specified for dictionary keys. Console.WriteLine() For Each s As String In keyColl Console.WriteLine("Key = {0}", s) Next s ' Use the Remove method to remove a key/value pair. Console.WriteLine(vbLf + "Remove(""doc"")") openWith.Remove("doc") If Not openWith.ContainsKey("doc") Then Console.WriteLine("Key ""doc"" is not found.") End If End Sub End Class ' This code example produces the following output: 'An element with Key = "txt" already exists. 'For key = "rtf", value = wordpad.exe. 'For key = "rtf", value = winword.exe. 'Key = "tif" is not found. 'Key = "tif" is not found. 'Value added for key = "ht": hypertrm.exe 'Key = txt, Value = notepad.exe 'Key = bmp, Value = paint.exe 'Key = dib, Value = paint.exe 'Key = rtf, Value = winword.exe 'Key = doc, Value = winword.exe 'Key = ht, Value = hypertrm.exe 'Value = notepad.exe 'Value = paint.exe 'Value = paint.exe 'Value = winword.exe 'Value = winword.exe 'Value = hypertrm.exe 'Key = txt 'Key = bmp 'Key = dib 'Key = rtf 'Key = doc 'Key = ht 'Remove("doc") 'Key "doc" is not found.

Remarks

The Dictionary<TKey,TValue> generic class provides a mapping from a set of keys to a set of values. Each addition to the dictionary consists of a value and its associated key. Retrieving a value by using its key is very fast, close to O(1), because the Dictionary<TKey,TValue> class is implemented as a hash table.

The speed of retrieval depends on the quality of the hashing algorithm of the type specified for TKey .

As long as an object is used as a key in the Dictionary<TKey,TValue> , it must not change in any way that affects its hash value. Every key in a Dictionary<TKey,TValue> must be unique according to the dictionary's equality comparer. A key cannot be null , but a value can be, if its type TValue is a reference type.

Dictionary<TKey,TValue> requires an equality implementation to determine whether keys are equal. You can specify an implementation of the IEqualityComparer<T> generic interface by using a constructor that accepts a comparer parameter; if you do not specify an implementation, the default generic equality comparer EqualityComparer<T>.Default is used. If type TKey implements the System.IEquatable<T> generic interface, the default equality comparer uses that implementation.

For example, you can use the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

The capacity of a Dictionary<TKey,TValue> is the number of elements the Dictionary<TKey,TValue> can hold. As elements are added to a Dictionary<TKey,TValue> , the capacity is automatically increased as required by reallocating the internal array.

.NET Framework only: For very large Dictionary<TKey,TValue> objects, you can increase the maximum capacity to 2 billion elements on a 64-bit system by setting the enabled attribute of the <gcAllowVeryLargeObjects> configuration element to true in the run-time environment.

For purposes of enumeration, each item in the dictionary is treated as a KeyValuePair<TKey,TValue> structure representing a value and its key. The order in which the items are returned is undefined.

The foreach statement of the C# language ( for each in C++, For Each in Visual Basic) returns an object of the type of the elements in the collection. Since the Dictionary<TKey,TValue> is a collection of keys and values, the element type is not the type of the key or the type of the value. Instead, the element type is a KeyValuePair<TKey,TValue> of the key type and the value type. For example:

for each(KeyValuePair<String^, String^> kvp in myDictionary) Console::WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value); foreach( KeyValuePair<string, string> kvp in myDictionary ) Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value); For Each kvp As KeyValuePair(Of String, String) In myDictionary Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value) Next kvp

The foreach statement is a wrapper around the enumerator, which allows only reading from the collection, not writing to it.

Because keys can be inherited and their behavior changed, their absolute uniqueness cannot be guaranteed by comparisons using the Equals method.

ToImmutableDictionary<TSource,TKey,TValue>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TValue>, IEqualityComparer<TKey>, IEqualityComparer<TValue>)

Enumerates and transforms a sequence, and produces an immutable dictionary of its contents by using the specified key and value comparers.

GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>, TResult>, IEqualityComparer<TKey>)

Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.

GroupJoin<TOuter,TInner,TKey,TResult>(IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter,TKey>, Func<TInner,TKey>, Func<TOuter,IEnumerable<TInner>, TResult>)

Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys.

GroupJoin<TOuter,TInner,TKey,TResult>(IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter,TKey>, Func<TInner,TKey>, Func<TOuter,IEnumerable<TInner>, TResult>, IEqualityComparer<TKey>)

Correlates the elements of two sequences based on key equality and groups the results. A specified IEqualityComparer<T> is used to compare keys.

Join<TOuter,TInner,TKey,TResult>(IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter,TKey>, Func<TInner,TKey>, Func<TOuter,TInner,TResult>, IEqualityComparer<TKey>)

Correlates the elements of two sequences based on matching keys. A specified IEqualityComparer<T> is used to compare keys.

Thread Safety

A Dictionary<TKey,TValue> can support multiple readers concurrently, as long as the collection is not modified. Even so, enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with write accesses, the collection must be locked during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

For thread-safe alternatives, see the ConcurrentDictionary<TKey,TValue> class or ImmutableDictionary<TKey,TValue> class.

Public static ( Shared in Visual Basic) members of this type are thread safe.

See also

  • IDictionary<TKey,TValue>
  • SortedList<TKey,TValue>
  • KeyValuePair<TKey,TValue>
  • IEqualityComparer<T>
  •