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>.
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.
| Exception | Condition |
|---|---|
| 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.
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.
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.
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 */
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
