.NET Framework Class Library
EnumerableToDictionaryTSource, TKey Method (IEnumerableTSource, FuncTSource, TKey)

Creates a DictionaryTKey, TValue from an IEnumerableT according to a specified key selector function.

Namespace:   System.Linq
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)
Syntax
<[%$TOPIC/bb549277_en-us_VS_110_3_0_0_0_0%]> _
Public Shared Function ToDictionary(Of TSource, TKey) ( _
	source As [%$TOPIC/bb549277_en-us_VS_110_3_0_0_0_1%](Of TSource), _
	keySelector As [%$TOPIC/bb549277_en-us_VS_110_3_0_0_0_2%](Of TSource, TKey) _
) As [%$TOPIC/bb549277_en-us_VS_110_3_0_0_0_3%](Of TKey, TSource)
public static [%$TOPIC/bb549277_en-us_VS_110_3_0_1_0_0%]<TKey, TSource> ToDictionary<TSource, TKey>(
	this [%$TOPIC/bb549277_en-us_VS_110_3_0_1_0_1%]<TSource> source,
	[%$TOPIC/bb549277_en-us_VS_110_3_0_1_0_2%]<TSource, TKey> keySelector
)
[[%$TOPIC/bb549277_en-us_VS_110_3_0_2_0_0%]]
public:
generic<typename TSource, typename TKey>
static [%$TOPIC/bb549277_en-us_VS_110_3_0_2_0_1%]<TKey, TSource>^ ToDictionary(
	[%$TOPIC/bb549277_en-us_VS_110_3_0_2_0_2%]<TSource>^ source, 
	[%$TOPIC/bb549277_en-us_VS_110_3_0_2_0_3%]<TSource, TKey>^ keySelector
)
static member ToDictionary : 
        source:[%$TOPIC/bb549277_en-us_VS_110_3_0_3_0_0%]<'TSource> * 
        keySelector:[%$TOPIC/bb549277_en-us_VS_110_3_0_3_0_1%]<'TSource, 'TKey> -> [%$TOPIC/bb549277_en-us_VS_110_3_0_3_0_2%]<'TKey, 'TSource> 
JScript does not support generic types or methods.

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

Parameters

source
Type: System.Collections.GenericIEnumerableTSource

An IEnumerableT to create a DictionaryTKey, TValue from.

keySelector
Type: SystemFuncTSource, TKey

A function to extract a key from each element.

Return Value

Type: System.Collections.GenericDictionaryTKey, TSource
A DictionaryTKey, TValue that contains keys and values.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerableTSource. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).
Exceptions
ExceptionCondition
ArgumentNullException

source or keySelector is .

-or-

keySelector produces a key that is .

ArgumentException

keySelector produces duplicate keys for two elements.

Remarks

The ToDictionaryTSource, TKey(IEnumerableTSource, FuncTSource, TKey) method uses the default equality comparer Default to compare keys.

Examples

The following code example demonstrates how to use ToDictionaryTSource, TKey(IEnumerableTSource, FuncTSource, TKey) to create a DictionaryTKey, TValue by using a key selector.

Structure Package
        Public Company As String 
        Public Weight As Double 
        Public TrackingNumber As Long 
    End Structure 

    Sub ToDictionaryEx1()
        ' Create a list of Package values. 
        Dim packages As New List(Of Package)(New Package() _
             {New Package With _
              {.Company = "Coho Vineyard", .Weight = 25.2, .TrackingNumber = 89453312L}, _
              New Package With _
              {.Company = "Lucerne Publishing", .Weight = 18.7, .TrackingNumber = 89112755L}, _
              New Package With _
              {.Company = "Wingtip Toys", .Weight = 6.0, .TrackingNumber = 299456122L}, _
              New Package With _
              {.Company = "Adventure Works", .Weight = 33.8, .TrackingNumber = 4665518773L}})

        ' Create a Dictionary that contains Package values,  
        ' using TrackingNumber as the key. 
        Dim dict As Dictionary(Of Long, Package) = _
            packages.ToDictionary(Function(p) p.TrackingNumber)

        ' Display the results. 
        Dim output As New System.Text.StringBuilder
        For Each kvp As KeyValuePair(Of Long, Package) In dict
            output.AppendLine("Key " & kvp.Key & ": " & _
                              kvp.Value.Company & ", " & _
                              kvp.Value.Weight & " pounds")
        Next
        MsgBox(output.ToString())
    End Sub 

    ' This code produces the following output: 
    ' 
    ' Key 89453312: Coho Vineyard, 25.2 pounds 
    ' Key 89112755: Lucerne Publishing, 18.7 pounds 
    ' Key 299456122: Wingtip Toys, 6 pounds 
    ' Key 4665518773: Adventure Works, 33.8 pounds
class Package
            {
                public string Company { get; set; }
                public double Weight { get; set; }
                public long TrackingNumber { get; set; }
            }

            public static void ToDictionaryEx1()
            {
                List<Package> packages =
                    new List<Package>
                        { new Package { Company = "Coho Vineyard", Weight = 25.2, TrackingNumber = 89453312L },
                          new Package { Company = "Lucerne Publishing", Weight = 18.7, TrackingNumber = 89112755L },
                          new Package { Company = "Wingtip Toys", Weight = 6.0, TrackingNumber = 299456122L },
                          new Package { Company = "Adventure Works", Weight = 33.8, TrackingNumber = 4665518773L } };

                // Create a Dictionary of Package objects,  
                // using TrackingNumber as the key.
                Dictionary<long, Package> dictionary =
                    packages.ToDictionary(p => p.TrackingNumber);

                foreach (KeyValuePair<long, Package> kvp in dictionary)
                {
                    Console.WriteLine(
                        "Key {0}: {1}, {2} pounds",
                        kvp.Key,
                        kvp.Value.Company,
                        kvp.Value.Weight);
                }
            }

            /*
             This code produces the following output:

             Key 89453312: Coho Vineyard, 25.2 pounds
             Key 89112755: Lucerne Publishing, 18.7 pounds
             Key 299456122: Wingtip Toys, 6 pounds
             Key 4665518773: Adventure Works, 33.8 pounds
            */
Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8