Enumerable.ToDictionary<(Of <(TSource, TKey, TElement>)>) Method (IEnumerable<(Of <(TSource>)>), Func<(Of <(TSource, TKey>)>), Func<(Of <(TSource, TElement>)>), IEqualityComparer<(Of <(TKey>)>))

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

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

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


<ExtensionAttribute> _
Public Shared Function ToDictionary(Of TSource, TKey, TElement) ( _
    source As IEnumerable(Of TSource), _
    keySelector As Func(Of TSource, TKey), _
    elementSelector As Func(Of TSource, TElement), _
    comparer As IEqualityComparer(Of TKey) _
) As Dictionary(Of TKey, TElement)
public static Dictionary<TKey, TElement> ToDictionary<TSource, TKey, TElement>(
    this IEnumerable<TSource> source,
    Func<TSource, TKey> keySelector,
    Func<TSource, TElement> elementSelector,
    IEqualityComparer<TKey> comparer

Type Parameters

  • TSource
    The type of the elements of source.
  • TKey
    The type of the key returned by keySelector.
  • TElement
    The type of the value returned by elementSelector.


  • keySelector
    Type: System..::.Func<(Of <(TSource, TKey>)>)
    A function to extract a key from each element.
  • elementSelector
    Type: System..::.Func<(Of <(TSource, TElement>)>)
    A transform function to produce a result element value from each element.

Return Value

Type: System.Collections.Generic..::.Dictionary<(Of <(TKey, TElement>)>)
A Dictionary<(Of <(TKey, TValue>)>) that contains values of type TElement selected from the input sequence.

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.


Exception Condition

source or keySelector or elementSelector is nullNothingnullptra null reference (Nothing in Visual Basic).


keySelector produces a key that is nullNothingnullptra null reference (Nothing in Visual Basic).


keySelector produces duplicate keys for two elements.


If comparer is nullNothingnullptra null reference (Nothing in Visual Basic), the default equality comparer Default is used to compare keys.

Version Information

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0


Windows Phone

See Also


Enumerable Class

ToDictionary Overload

System.Linq Namespace