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Enumerable.ToDictionary(Of TSource, TKey) Method (IEnumerable(Of TSource), Func(Of TSource, TKey))

Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to a specified key selector function.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

<ExtensionAttribute> _
Public Shared Function ToDictionary(Of TSource, TKey) ( _
	source As IEnumerable(Of TSource), _
	keySelector As Func(Of TSource, TKey) _
) As Dictionary(Of TKey, TSource)

Type Parameters


The type of the elements of source.


The type of the key returned by keySelector.


Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to create a Dictionary(Of TKey, TValue) from.
Type: System.Func(Of TSource, TKey)
A function to extract a key from each element.

Return Value

Type: System.Collections.Generic.Dictionary(Of TKey, TSource)
A Dictionary(Of TKey, 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 IEnumerable(Of TSource). When you use instance method syntax to call this method, omit the first parameter.


source or keySelector is Nothing.


keySelector produces a key that is Nothing.


keySelector produces duplicate keys for two elements.

The ToDictionary(Of TSource, TKey)(IEnumerable(Of TSource), Func(Of TSource, TKey)) method uses the default equality comparer Default to compare keys.

The following code example demonstrates how to use ToDictionary(Of TSource, TKey)(IEnumerable(Of TSource), Func(Of TSource, TKey)) to create a Dictionary(Of TKey, 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")
      outputBlock.Text &= output.ToString() & vbCrLf
   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


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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