Dictionary<TKey,TValue> Constructors

Reference

Definition

Namespace:: System.Collections.Generic

Assembly:: System.Collections.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Initializes a new instance of the Dictionary<TKey,TValue> class.

Overloads

Dictionary<TKey,TValue>()	Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the default initial capacity, and uses the default equality comparer for the key type.
Dictionary<TKey,TValue>(IDictionary<TKey,TValue>)	Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IDictionary<TKey,TValue> and uses the default equality comparer for the key type.
Dictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>)	Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IEnumerable<T>.
Dictionary<TKey,TValue>(IEqualityComparer<TKey>)	Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the default initial capacity, and uses the specified IEqualityComparer<T>.
Dictionary<TKey,TValue>(Int32)	Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the specified initial capacity, and uses the default equality comparer for the key type.
Dictionary<TKey,TValue>(IDictionary<TKey,TValue>, IEqualityComparer<TKey>)	Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IDictionary<TKey,TValue> and uses the specified IEqualityComparer<T>.
Dictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>, IEqualityComparer<TKey>)	Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IEnumerable<T> and uses the specified IEqualityComparer<T>.
Dictionary<TKey,TValue>(Int32, IEqualityComparer<TKey>)	Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the specified initial capacity, and uses the specified IEqualityComparer<T>.
Dictionary<TKey,TValue>(SerializationInfo, StreamingContext)	Obsolete. Initializes a new instance of the Dictionary<TKey,TValue> class with serialized data.

Dictionary<TKey,TValue>()

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the default initial capacity, and uses the default equality comparer for the key type.

public:
 Dictionary();

public Dictionary ();

Public Sub New ()

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.

This code example is part of a larger example provided for the Dictionary<TKey,TValue> class.

// 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.
try
{
    openWith->Add("txt", "winword.exe");
}
catch (ArgumentException^)
{
    Console::WriteLine("An element with Key = \"txt\" already exists.");
}

// 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.
try
{
    openWith.Add("txt", "winword.exe");
}
catch (ArgumentException)
{
    Console.WriteLine("An element with Key = \"txt\" already exists.");
}

// Create a new dictionary of strings, with string keys.
let openWith = 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.
try
    openWith.Add("txt", "winword.exe")
with :? ArgumentException ->
    printfn "An element with Key = \"txt\" already exists."

' 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.
Try
    openWith.Add("txt", "winword.exe")
Catch 
    Console.WriteLine("An element with Key = ""txt"" already exists.")
End Try

Remarks

Every key in a Dictionary<TKey,TValue> must be unique according to the default equality comparer.

Dictionary<TKey,TValue> requires an equality implementation to determine whether keys are equal. This constructor uses the default generic equality comparer, EqualityComparer<T>.Default. If type TKey implements the System.IEquatable<T> generic interface, the default equality comparer uses that implementation. Alternatively, you can specify an implementation of the IEqualityComparer<T> generic interface by using a constructor that accepts a comparer parameter.

Note

If you can estimate the size of the collection, using a constructor that specifies the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Dictionary<TKey,TValue>.

This constructor is an O(1) operation.

Applies to

Dictionary<TKey,TValue>(IDictionary<TKey,TValue>)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IDictionary<TKey,TValue> and uses the default equality comparer for the key type.

public:
 Dictionary(System::Collections::Generic::IDictionary<TKey, TValue> ^ dictionary);

public Dictionary (System.Collections.Generic.IDictionary<TKey,TValue> dictionary);

new System.Collections.Generic.Dictionary<'Key, 'Value> : System.Collections.Generic.IDictionary<'Key, 'Value> -> System.Collections.Generic.Dictionary<'Key, 'Value>

Public Sub New (dictionary As IDictionary(Of TKey, TValue))

Parameters

dictionary: IDictionary<TKey,TValue>

The IDictionary<TKey,TValue> whose elements are copied to the new Dictionary<TKey,TValue>.

Exceptions

ArgumentNullException

dictionary is null.

ArgumentException

dictionary contains one or more duplicate keys.

Examples

The following code example shows how to use the Dictionary<TKey,TValue>(IEqualityComparer<TKey>) constructor to initialize a Dictionary<TKey,TValue> with sorted content from another dictionary. The code example creates a SortedDictionary<TKey,TValue> and populates it with data in random order, then passes the SortedDictionary<TKey,TValue> to the Dictionary<TKey,TValue>(IEqualityComparer<TKey>) constructor, creating a Dictionary<TKey,TValue> that is sorted. This is useful if you need to build a sorted dictionary that at some point becomes static; copying the data from a SortedDictionary<TKey,TValue> to a Dictionary<TKey,TValue> improves retrieval speed.

using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        // Create a new sorted dictionary of strings, with string
        // keys.
        SortedDictionary<string, string> openWith =
            new SortedDictionary<string, string>();

        // Add some elements to the dictionary.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("dib", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");

        // Create a Dictionary of strings with string keys, and
        // initialize it with the contents of the sorted dictionary.
        Dictionary<string, string> copy =
            new Dictionary<string, string>(openWith);

        // List the contents of the copy.
        Console.WriteLine();
        foreach( KeyValuePair<string, string> kvp in copy )
        {
            Console.WriteLine("Key = {0}, Value = {1}",
               kvp.Key, kvp.Value);
        }
    }
}

/* This code example produces the following output:

Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = wordpad.exe
Key = txt, Value = notepad.exe
 */

open System.Collections.Generic

// Create a new sorted dictionary of strings, with string
// keys.
let openWith = SortedDictionary<string, string>()

// Add some elements to the dictionary.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("dib", "paint.exe")
openWith.Add("rtf", "wordpad.exe")

// Create a Dictionary of strings with string keys, and
// initialize it with the contents of the sorted dictionary.
let copy = Dictionary<string, string> openWith

// List the contents of the copy.
printfn ""

for kvp in copy do
    printfn $"Key = {kvp.Key}, Value = {kvp.Value}"
// This code example produces the following output:
//     Key = bmp, Value = paint.exe
//     Key = dib, Value = paint.exe
//     Key = rtf, Value = wordpad.exe
//     Key = txt, Value = notepad.exe

Imports System.Collections.Generic

Public Class Example
    
    Public Shared Sub Main() 

        ' Create a new sorted dictionary of strings, with string 
        ' keys.
        Dim openWith As New SortedDictionary(Of String, String)
        
        ' Add some elements to the sorted dictionary. 
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("dib", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")
        
        ' Create a Dictionary of strings with string keys, and 
        ' initialize it with the contents of the sorted dictionary.
        Dim copy As New Dictionary(Of String, String)(openWith)

        ' List the contents of the copy.
        Console.WriteLine()
        For Each kvp As KeyValuePair(Of String, String) In copy
            Console.WriteLine("Key = {0}, Value = {1}", _
                kvp.Key, kvp.Value)
        Next kvp

    End Sub

End Class

' This code example produces the following output:
'
'Key = bmp, Value = paint.exe
'Key = dib, Value = paint.exe
'Key = rtf, Value = wordpad.exe
'Key = txt, Value = notepad.exe

Remarks

Every key in a Dictionary<TKey,TValue> must be unique according to the default equality comparer; likewise, every key in the source dictionary must also be unique according to the default equality comparer.

The initial capacity of the new Dictionary<TKey,TValue> is large enough to contain all the elements in dictionary.

This constructor is an O(n) operation, where n is the number of elements in dictionary.

Applies to

Dictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IEnumerable<T>.

public:
 Dictionary(System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>> ^ collection);

public Dictionary (System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>> collection);

new System.Collections.Generic.Dictionary<'Key, 'Value> : seq<System.Collections.Generic.KeyValuePair<'Key, 'Value>> -> System.Collections.Generic.Dictionary<'Key, 'Value>

Public Sub New (collection As IEnumerable(Of KeyValuePair(Of TKey, TValue)))

Parameters

collection: IEnumerable<KeyValuePair<TKey,TValue>>

The IEnumerable<T> whose elements are copied to the new Dictionary<TKey,TValue>.

Exceptions

ArgumentNullException

collection is null.

ArgumentException

collection contains one or more duplicated keys.

Applies to

Dictionary<TKey,TValue>(IEqualityComparer<TKey>)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the default initial capacity, and uses the specified IEqualityComparer<T>.

public:
 Dictionary(System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public Dictionary (System.Collections.Generic.IEqualityComparer<TKey> comparer);

public Dictionary (System.Collections.Generic.IEqualityComparer<TKey>? comparer);

new System.Collections.Generic.Dictionary<'Key, 'Value> : System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Value>

Public Sub New (comparer As IEqualityComparer(Of TKey))

Parameters

comparer: IEqualityComparer<TKey>

The IEqualityComparer<T> implementation to use when comparing keys, or null to use the default EqualityComparer<T> for the type of the key.

Examples

The following code example creates a Dictionary<TKey,TValue> with a case-insensitive equality comparer for the current culture. The example adds four elements, some with lower-case keys and some with upper-case keys. The example then attempts to add an element with a key that differs from an existing key only by case, catches the resulting exception, and displays an error message. Finally, the example displays the elements in the dictionary.

using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        // Create a new Dictionary of strings, with string keys
        // and a case-insensitive comparer for the current culture.
        Dictionary<string, string> openWith =
                      new Dictionary<string, string>(
                          StringComparer.CurrentCultureIgnoreCase);

        // Add some elements to the dictionary.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("DIB", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");

        // Try to add a fifth element with a key that is the same
        // except for case; this would be allowed with the default
        // comparer.
        try
        {
            openWith.Add("BMP", "paint.exe");
        }
        catch (ArgumentException)
        {
            Console.WriteLine("\nBMP is already in the dictionary.");
        }

        // List the contents of the sorted dictionary.
        Console.WriteLine();
        foreach( KeyValuePair<string, string> kvp in openWith )
        {
            Console.WriteLine("Key = {0}, Value = {1}", kvp.Key,
                kvp.Value);
        }
    }
}

/* This code example produces the following output:

BMP is already in the dictionary.

Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = DIB, Value = paint.exe
Key = rtf, Value = wordpad.exe
 */

open System
open System.Collections.Generic

// Create a new Dictionary of strings, with string keys
// and a case-insensitive comparer for the current culture.
let openWith = Dictionary<string, string> StringComparer.CurrentCultureIgnoreCase

// Add some elements to the dictionary.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("DIB", "paint.exe")
openWith.Add("rtf", "wordpad.exe")

// Try to add a fifth element with a key that is the same
// except for case; this would be allowed with the default
// comparer.
try
    openWith.Add("BMP", "paint.exe")
with :? ArgumentException ->
    printfn "\nBMP is already in the dictionary."

// List the contents of the sorted dictionary.
printfn ""

for kvp in openWith do
    printfn $"Key = {kvp.Key}, Value = {kvp.Value}"
// This code example produces the following output:
//     BMP is already in the dictionary.
//
//     Key = txt, Value = notepad.exe
//     Key = bmp, Value = paint.exe
//     Key = DIB, Value = paint.exe
//     Key = rtf, Value = wordpad.exe

Imports System.Collections.Generic

Public Class Example
    
    Public Shared Sub Main() 

        ' Create a new Dictionary of strings, with string keys 
        ' and a case-insensitive comparer for the current culture.
        Dim openWith As New Dictionary(Of String, String)( _
            StringComparer.CurrentCultureIgnoreCase)
        
        ' Add some elements to the dictionary. 
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("DIB", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")

        ' Try to add a fifth element with a key that is the same 
        ' except for case; this would be allowed with the default
        ' comparer.
        Try
            openWith.Add("BMP", "paint.exe")
        Catch ex As ArgumentException
            Console.WriteLine(vbLf & "BMP is already in the dictionary.")
        End Try
        
        ' List the contents of the dictionary.
        Console.WriteLine()
        For Each kvp As KeyValuePair(Of String, String) In openWith
            Console.WriteLine("Key = {0}, Value = {1}", _
                kvp.Key, kvp.Value)
        Next kvp

    End Sub

End Class

' This code example produces the following output:
'
'BMP is already in the dictionary.
'
'Key = txt, Value = notepad.exe
'Key = bmp, Value = paint.exe
'Key = DIB, Value = paint.exe
'Key = rtf, Value = wordpad.exe

Remarks

Use this constructor with the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

Every key in a Dictionary<TKey,TValue> must be unique according to the specified comparer.

Dictionary<TKey,TValue> requires an equality implementation to determine whether keys are equal. If comparer is null, this constructor uses the default generic equality comparer, EqualityComparer<T>.Default. If type TKey implements the System.IEquatable<T> generic interface, the default equality comparer uses that implementation.

Note

This constructor is an O(1) operation.

Applies to

Dictionary<TKey,TValue>(Int32)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the specified initial capacity, and uses the default equality comparer for the key type.

public:
 Dictionary(int capacity);

public Dictionary (int capacity);

new System.Collections.Generic.Dictionary<'Key, 'Value> : int -> System.Collections.Generic.Dictionary<'Key, 'Value>

Public Sub New (capacity As Integer)

Parameters

capacity: Int32

The initial number of elements that the Dictionary<TKey,TValue> can contain.

Exceptions

ArgumentOutOfRangeException

capacity is less than 0.

Examples

The following code example creates a dictionary with an initial capacity of 4 and populates it with 4 entries.

using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        // Create a new dictionary of strings, with string keys and
        // an initial capacity of 4.
        Dictionary<string, string> openWith =
                               new Dictionary<string, string>(4);

        // Add 4 elements to the dictionary.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("dib", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");

        // List the contents of the dictionary.
        Console.WriteLine();
        foreach( KeyValuePair<string, string> kvp in openWith )
        {
            Console.WriteLine("Key = {0}, Value = {1}",
               kvp.Key, kvp.Value);
        }
    }
}

/* This code example produces the following output:

Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = wordpad.exe
 */

open System.Collections.Generic

// Create a new dictionary of strings, with string keys and
// an initial capacity of 4.
let openWith = Dictionary<string, string> 4

// Add 4 elements to the dictionary.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("dib", "paint.exe")
openWith.Add("rtf", "wordpad.exe")

// List the contents of the dictionary.
printfn ""

for kvp in openWith do
    printfn $"Key = {kvp.Key}, Value = {kvp.Value}"
// This code example produces the following output:
//     Key = txt, Value = notepad.exe
//     Key = bmp, Value = paint.exe
//     Key = dib, Value = paint.exe
//     Key = rtf, Value = wordpad.exe

Imports System.Collections.Generic

Public Class Example
    
    Public Shared Sub Main() 

        ' Create a new dictionary of strings, with string keys and
        ' an initial capacity of 4.
        Dim openWith As New Dictionary(Of String, String)(4)
        
        ' Add 4 elements to the dictionary. 
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("dib", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")
        
        ' List the contents of the dictionary.
        Console.WriteLine()
        For Each kvp As KeyValuePair(Of String, String) In openWith
            Console.WriteLine("Key = {0}, Value = {1}", _
                kvp.Key, kvp.Value)
        Next kvp

    End Sub

End Class

' This code example produces the following output:
'
'Key = txt, Value = notepad.exe
'Key = bmp, Value = paint.exe
'Key = dib, Value = paint.exe
'Key = rtf, Value = wordpad.exe

Remarks

Every key in a Dictionary<TKey,TValue> must be unique according to the default equality comparer.

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

If the size of the collection can be estimated, specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Dictionary<TKey,TValue>.

This constructor is an O(1) operation.

Applies to

Dictionary<TKey,TValue>(IDictionary<TKey,TValue>, IEqualityComparer<TKey>)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IDictionary<TKey,TValue> and uses the specified IEqualityComparer<T>.

public:
 Dictionary(System::Collections::Generic::IDictionary<TKey, TValue> ^ dictionary, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public Dictionary (System.Collections.Generic.IDictionary<TKey,TValue> dictionary, System.Collections.Generic.IEqualityComparer<TKey> comparer);

public Dictionary (System.Collections.Generic.IDictionary<TKey,TValue> dictionary, System.Collections.Generic.IEqualityComparer<TKey>? comparer);

new System.Collections.Generic.Dictionary<'Key, 'Value> : System.Collections.Generic.IDictionary<'Key, 'Value> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Value>

Public Sub New (dictionary As IDictionary(Of TKey, TValue), comparer As IEqualityComparer(Of TKey))

Parameters

dictionary: IDictionary<TKey,TValue>

The IDictionary<TKey,TValue> whose elements are copied to the new Dictionary<TKey,TValue>.

comparer: IEqualityComparer<TKey>

The IEqualityComparer<T> implementation to use when comparing keys, or null to use the default EqualityComparer<T> for the type of the key.

Exceptions

ArgumentNullException

dictionary is null.

ArgumentException

dictionary contains one or more duplicate keys.

Examples

The following code example shows how to use the Dictionary<TKey,TValue>(IDictionary<TKey,TValue>, IEqualityComparer<TKey>) constructor to initialize a Dictionary<TKey,TValue> with case-insensitive sorted content from another dictionary. The code example creates a SortedDictionary<TKey,TValue> with a case-insensitive comparer and populates it with data in random order, then passes the SortedDictionary<TKey,TValue> to the Dictionary<TKey,TValue>(IDictionary<TKey,TValue>, IEqualityComparer<TKey>) constructor, along with a case-insensitive equality comparer, creating a Dictionary<TKey,TValue> that is sorted. This is useful if you need to build a sorted dictionary that at some point becomes static; copying the data from a SortedDictionary<TKey,TValue> to a Dictionary<TKey,TValue> improves retrieval speed.

Note

When you create a new dictionary with a case-insensitive comparer and populate it with entries from a dictionary that uses a case-sensitive comparer, as in this example, an exception occurs if the input dictionary has keys that differ only by case.

using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        // Create a new sorted dictionary of strings, with string
        // keys and a case-insensitive comparer.
        SortedDictionary<string, string> openWith =
                new SortedDictionary<string, string>(
                    StringComparer.CurrentCultureIgnoreCase);

        // Add some elements to the dictionary.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("Bmp", "paint.exe");
        openWith.Add("DIB", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");

        // Create a Dictionary of strings with string keys and a
        // case-insensitive equality comparer, and initialize it
        // with the contents of the sorted dictionary.
        Dictionary<string, string> copy =
                new Dictionary<string, string>(openWith,
                    StringComparer.CurrentCultureIgnoreCase);

        // List the contents of the copy.
        Console.WriteLine();
        foreach( KeyValuePair<string, string> kvp in copy )
        {
            Console.WriteLine("Key = {0}, Value = {1}",
               kvp.Key, kvp.Value);
        }
    }
}

/* This code example produces the following output:

Key = Bmp, Value = paint.exe
Key = DIB, Value = paint.exe
Key = rtf, Value = wordpad.exe
Key = txt, Value = notepad.exe
 */

open System
open System.Collections.Generic

// Create a new sorted dictionary of strings, with string
// keys and a case-insensitive comparer.
let openWith =
    SortedDictionary<string, string> StringComparer.CurrentCultureIgnoreCase

// Add some elements to the dictionary.
openWith.Add("txt", "notepad.exe")
openWith.Add("Bmp", "paint.exe")
openWith.Add("DIB", "paint.exe")
openWith.Add("rtf", "wordpad.exe")

// Create a Dictionary of strings with string keys and a
// case-insensitive equality comparer, and initialize it
// with the contents of the sorted dictionary.
let copy =
    Dictionary<string, string>(openWith, StringComparer.CurrentCultureIgnoreCase)

// List the contents of the copy.
printfn ""

for kvp in copy do
    printfn $"Key = {kvp.Key}, Value = {kvp.Value}"
// This code example produces the following output:
//     Key = Bmp, Value = paint.exe
//     Key = DIB, Value = paint.exe
//     Key = rtf, Value = wordpad.exe
//     Key = txt, Value = notepad.exe

Imports System.Collections.Generic

Public Class Example
    
    Public Shared Sub Main() 

        ' Create a new sorted dictionary of strings, with string 
        ' keys and a case-insensitive comparer.
        Dim openWith As New SortedDictionary(Of String, String)( _
            StringComparer.CurrentCultureIgnoreCase)
        
        ' Add some elements to the sorted dictionary. 
        openWith.Add("txt", "notepad.exe")
        openWith.Add("Bmp", "paint.exe")
        openWith.Add("DIB", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")
        
        ' Create a Dictionary of strings with string keys and a 
        ' case-insensitive equality comparer, and initialize it
        ' with the contents of the sorted dictionary.
        Dim copy As New Dictionary(Of String, String)(openWith, _
            StringComparer.CurrentCultureIgnoreCase)

        ' List the contents of the copy.
        Console.WriteLine()
        For Each kvp As KeyValuePair(Of String, String) In copy
            Console.WriteLine("Key = {0}, Value = {1}", _
                kvp.Key, kvp.Value)
        Next kvp

    End Sub

End Class

' This code example produces the following output:
'
'Key = Bmp, Value = paint.exe
'Key = DIB, Value = paint.exe
'Key = rtf, Value = wordpad.exe
'Key = txt, Value = notepad.exe

Remarks

Use this constructor with the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

Every key in a Dictionary<TKey,TValue> must be unique according to the specified comparer; likewise, every key in the source dictionary must also be unique according to the specified comparer.

Note

For example, duplicate keys can occur if comparer is one of the case-insensitive string comparers provided by the StringComparer class and dictionary does not use a case-insensitive comparer key.

The initial capacity of the new Dictionary<TKey,TValue> is large enough to contain all the elements in dictionary.

This constructor is an O(n) operation, where n is the number of elements in dictionary.

Applies to

Dictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>, IEqualityComparer<TKey>)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that contains elements copied from the specified IEnumerable<T> and uses the specified IEqualityComparer<T>.

public:
 Dictionary(System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>> ^ collection, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public Dictionary (System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>> collection, System.Collections.Generic.IEqualityComparer<TKey>? comparer);

public Dictionary (System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>> collection, System.Collections.Generic.IEqualityComparer<TKey> comparer);

new System.Collections.Generic.Dictionary<'Key, 'Value> : seq<System.Collections.Generic.KeyValuePair<'Key, 'Value>> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Value>

Public Sub New (collection As IEnumerable(Of KeyValuePair(Of TKey, TValue)), comparer As IEqualityComparer(Of TKey))

Parameters

collection: IEnumerable<KeyValuePair<TKey,TValue>>

The IEnumerable<T> whose elements are copied to the new Dictionary<TKey,TValue>.

comparer: IEqualityComparer<TKey>

The IEqualityComparer<T> implementation to use when comparing keys, or null to use the default EqualityComparer<T> for the type of the key.

Exceptions

ArgumentNullException

collection is null.

ArgumentException

collection contains one or more duplicated keys.

Applies to

Dictionary<TKey,TValue>(Int32, IEqualityComparer<TKey>)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Initializes a new instance of the Dictionary<TKey,TValue> class that is empty, has the specified initial capacity, and uses the specified IEqualityComparer<T>.

public:
 Dictionary(int capacity, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public Dictionary (int capacity, System.Collections.Generic.IEqualityComparer<TKey> comparer);

public Dictionary (int capacity, System.Collections.Generic.IEqualityComparer<TKey>? comparer);

new System.Collections.Generic.Dictionary<'Key, 'Value> : int * System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Value>

Public Sub New (capacity As Integer, comparer As IEqualityComparer(Of TKey))

Parameters

capacity: Int32

The initial number of elements that the Dictionary<TKey,TValue> can contain.

comparer: IEqualityComparer<TKey>

The IEqualityComparer<T> implementation to use when comparing keys, or null to use the default EqualityComparer<T> for the type of the key.

Exceptions

ArgumentOutOfRangeException

capacity is less than 0.

Examples

The following code example creates a Dictionary<TKey,TValue> with an initial capacity of 5 and a case-insensitive equality comparer for the current culture. The example adds four elements, some with lower-case keys and some with upper-case keys. The example then attempts to add an element with a key that differs from an existing key only by case, catches the resulting exception, and displays an error message. Finally, the example displays the elements in the dictionary.

using System;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        // Create a new dictionary of strings, with string keys, an
        // initial capacity of 5, and a case-insensitive equality
        // comparer.
        Dictionary<string, string> openWith =
                      new Dictionary<string, string>(5,
                          StringComparer.CurrentCultureIgnoreCase);

        // Add 4 elements to the dictionary.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("DIB", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");

        // Try to add a fifth element with a key that is the same
        // except for case; this would be allowed with the default
        // comparer.
        try
        {
            openWith.Add("BMP", "paint.exe");
        }
        catch (ArgumentException)
        {
            Console.WriteLine("\nBMP is already in the dictionary.");
        }

        // List the contents of the dictionary.
        Console.WriteLine();
        foreach( KeyValuePair<string, string> kvp in openWith )
        {
            Console.WriteLine("Key = {0}, Value = {1}", kvp.Key,
                kvp.Value);
        }
    }
}

/* This code example produces the following output:

BMP is already in the dictionary.

Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = DIB, Value = paint.exe
Key = rtf, Value = wordpad.exe
 */

open System
open System.Collections.Generic

// Create a new dictionary of strings, with string keys, an
// initial capacity of 5, and a case-insensitive equality
// comparer.
let openWith =
    Dictionary<string, string>(5, StringComparer.CurrentCultureIgnoreCase)

// Add 4 elements to the dictionary.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("DIB", "paint.exe")
openWith.Add("rtf", "wordpad.exe")

// Try to add a fifth element with a key that is the same
// except for case; this would be allowed with the default
// comparer.
try
    openWith.Add("BMP", "paint.exe")
with :? ArgumentException ->
    printfn "\nBMP is already in the dictionary."

// List the contents of the dictionary.
printfn ""

for kvp in openWith do
    printfn $"Key = {kvp.Key}, Value = {kvp.Value}"
// This code example produces the following output:
//     BMP is already in the dictionary.
//
//     Key = txt, Value = notepad.exe
//     Key = bmp, Value = paint.exe
//     Key = DIB, Value = paint.exe
//     Key = rtf, Value = wordpad.exe

Imports System.Collections.Generic

Public Class Example
    
    Public Shared Sub Main() 

        ' Create a new Dictionary of strings, with string keys, an
        ' initial capacity of 5, and a case-insensitive equality
        ' comparer.
        Dim openWith As New Dictionary(Of String, String)(5, _
            StringComparer.CurrentCultureIgnoreCase)
        
        ' Add 4 elements to the dictionary. 
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("DIB", "paint.exe")
        openWith.Add("rtf", "wordpad.exe")

        ' Try to add a fifth element with a key that is the same 
        ' except for case; this would be allowed with the default
        ' comparer.
        Try
            openWith.Add("BMP", "paint.exe")
        Catch ex As ArgumentException
            Console.WriteLine(vbLf & "BMP is already in the dictionary.")
        End Try
        
        ' List the contents of the dictionary.
        Console.WriteLine()
        For Each kvp As KeyValuePair(Of String, String) In openWith
            Console.WriteLine("Key = {0}, Value = {1}", _
                kvp.Key, kvp.Value)
        Next kvp

    End Sub

End Class

' This code example produces the following output:
'
'BMP is already in the dictionary.
'
'Key = txt, Value = notepad.exe
'Key = bmp, Value = paint.exe
'Key = DIB, Value = paint.exe
'Key = rtf, Value = wordpad.exe

Remarks

Use this constructor with the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

Every key in a Dictionary<TKey,TValue> must be unique according to the specified comparer.

If the size of the collection can be estimated, specifying the initial capacity eliminates the need to perform a number of resizing operations while adding elements to the Dictionary<TKey,TValue>.

This constructor is an O(1) operation.

Applies to

Dictionary<TKey,TValue>(SerializationInfo, StreamingContext)

Source:: Dictionary.cs

Source:: Dictionary.cs

Source:: Dictionary.cs

Caution

This API supports obsolete formatter-based serialization. It should not be called or extended by application code.

Initializes a new instance of the Dictionary<TKey,TValue> class with serialized data.

protected:
 Dictionary(System::Runtime::Serialization::SerializationInfo ^ info, System::Runtime::Serialization::StreamingContext context);

protected Dictionary (System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context);

[System.Obsolete("This API supports obsolete formatter-based serialization. It should not be called or extended by application code.", DiagnosticId="SYSLIB0051", UrlFormat="https://aka.ms/dotnet-warnings/{0}")]
protected Dictionary (System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context);

new System.Collections.Generic.Dictionary<'Key, 'Value> : System.Runtime.Serialization.SerializationInfo * System.Runtime.Serialization.StreamingContext -> System.Collections.Generic.Dictionary<'Key, 'Value>

[<System.Obsolete("This API supports obsolete formatter-based serialization. It should not be called or extended by application code.", DiagnosticId="SYSLIB0051", UrlFormat="https://aka.ms/dotnet-warnings/{0}")>]
new System.Collections.Generic.Dictionary<'Key, 'Value> : System.Runtime.Serialization.SerializationInfo * System.Runtime.Serialization.StreamingContext -> System.Collections.Generic.Dictionary<'Key, 'Value>

Protected Sub New (info As SerializationInfo, context As StreamingContext)

Parameters

info: SerializationInfo

A SerializationInfo object containing the information required to serialize the Dictionary<TKey,TValue>.

context: StreamingContext

A StreamingContext structure containing the source and destination of the serialized stream associated with the Dictionary<TKey,TValue>.

Attributes: ObsoleteAttribute

Remarks

This constructor is called during deserialization to reconstitute an object transmitted over a stream. For more information, see XML and SOAP Serialization.

Applies to

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Dictionary<TKey,TValue> Constructors

Definition

Overloads

Dictionary<TKey,TValue>()

Examples

Remarks

See also

Applies to

Dictionary<TKey,TValue>(IDictionary<TKey,TValue>)

Parameters

Exceptions

Examples

Remarks

See also

Applies to

Dictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>)

Parameters

Exceptions

Applies to

Dictionary<TKey,TValue>(IEqualityComparer<TKey>)

Parameters

Examples

Remarks

See also

Applies to

Dictionary<TKey,TValue>(Int32)

Parameters

Exceptions

Examples

Remarks

See also

Applies to

Dictionary<TKey,TValue>(IDictionary<TKey,TValue>, IEqualityComparer<TKey>)

Parameters

Exceptions

Examples

Remarks

See also

Applies to

Dictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>, IEqualityComparer<TKey>)

Parameters

Exceptions

Applies to

Dictionary<TKey,TValue>(Int32, IEqualityComparer<TKey>)

Parameters

Exceptions

Examples

Remarks

See also

Applies to

Dictionary<TKey,TValue>(SerializationInfo, StreamingContext)

Parameters

Remarks

See also

Applies to

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