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.
Assembly: System.Core (in System.Core.dll)
'Declaration <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
- TSource
The type of the elements of source.
- TKey
The type of the key returned by keySelector.
Parameters
- source
- Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to create a Dictionary(Of TKey, TValue) from.
- keySelector
- 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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).| Exception | Condition |
|---|---|
| ArgumentNullException | source or keySelector is Nothing. -or- keySelector produces a key that is Nothing. |
| ArgumentException | 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")
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
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.