Enumerable.ToDictionary<TSource, TKey> Method (IEnumerable<TSource>, Func<TSource, TKey>)
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Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
'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)
public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey>(
this IEnumerable<TSource> source,
Func<TSource, TKey> keySelector
)
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<TSource>
An IEnumerable<T> to create a Dictionary<TKey, TValue> from.
- keySelector
Type: System.Func<TSource, TKey>
A function to extract a key from each element.
Return Value
Type: System.Collections.Generic.Dictionary<TKey, TSource>
A Dictionary<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<TSource>. When you use instance method syntax to call this method, omit the first parameter.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | source or keySelector is nulla null reference (Nothing in Visual Basic). -or- keySelector produces a key that is nulla null reference (Nothing in Visual Basic). |
| ArgumentException | keySelector produces duplicate keys for two elements. |
Remarks
The ToDictionary<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>) method uses the default equality comparer Default to compare keys.
Examples
The following code example demonstrates how to use ToDictionary<TSource, TKey>(IEnumerable<TSource>, Func<TSource, TKey>) to create a Dictionary<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
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
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)
{
outputBlock.Text += String.Format(
"Key {0}: {1}, {2} pounds",
kvp.Key,
kvp.Value.Company,
kvp.Value.Weight) + "\n";
}
}
/*
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
Silverlight
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
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.