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EnumerableToDictionary Method
 

Creates a Dictionary from an IEnumerable according to a specified key selector function.

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

public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey>(
	this IEnumerable<TSource> source,
	Func<TSource, TKey> keySelector
)
public:
generic<typename TSource, typename TKey>
[ExtensionAttribute]
static Dictionary<TKey, TSource>^ ToDictionary(
	IEnumerable<TSource>^ source,
	Func<TSource, TKey>^ keySelector
)
static member ToDictionary<'TSource, 'TKey> : 
        source:IEnumerable<'TSource> *
        keySelector:Func<'TSource, 'TKey> -> Dictionary<'TKey, 'TSource>
<ExtensionAttribute>
Public Shared Function ToDictionary(Of TSource, TKey) (
	source As IEnumerable(Of TSource),
	keySelector As Func(Of TSource, TKey)
) As Dictionary(Of TKey, TSource)

Parameters

source
Type:

An IEnumerable to create a Dictionary from.

keySelector
Type:

A function to extract a key from each element.

Return Value

Type:

A Dictionary that contains keys and values.

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

Exception Condition
ArgumentNullException

source or keySelector is null.

-or-

keySelector produces a key that is null.

ArgumentException

keySelector produces duplicate keys for two elements.

The ToDictionary method uses the default equality comparer to compare keys.

The following code example demonstrates how to use ToDictionary to create a Dictionary by using a key selector.

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
*/
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
Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
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
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