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Dictionary<TKey, TValue> Constructor (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>.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

public Dictionary(
	IDictionary<TKey, TValue> dictionary,
	IEqualityComparer<TKey> comparer
)

Parameters

dictionary
Type: System.Collections.Generic.IDictionary<TKey, TValue>

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

comparer
Type: System.Collections.Generic.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.

ExceptionCondition
ArgumentNullException

dictionary is null.

ArgumentException

dictionary contains one or more duplicate keys.

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.

NoteNote

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.

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.

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

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.

NoteNote

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
 */

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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