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Enumerable.ToDictionary Method

  • Reference

Definition

Namespace:
System.Linq
Assembly:
System.Linq.dll
Assembly:
System.Core.dll
Assembly:
netstandard.dll

Creates a Dictionary<TKey,TValue> from an IEnumerable<T>.

Overloads

ToDictionary<TKey,TValue>(IEnumerable<ValueTuple<TKey,TValue>>, IEqualityComparer<TKey>)

Creates a dictionary from an enumeration according to specified key equality comparer.
ToDictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>, IEqualityComparer<TKey>)

Creates a dictionary from an enumeration according to specified key comparer.
ToDictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>)

Creates a dictionary from an enumeration according to the default comparer for the key type.
ToDictionary<TKey,TValue>(IEnumerable<ValueTuple<TKey,TValue>>)

Creates a dictionary from an enumeration according to the default comparer for the key type.
ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)

Creates a Dictionary<TKey,TValue> from an IEnumerable<T> according to specified key selector and element selector functions.
ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)

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

Creates a Dictionary<TKey,TValue> from an IEnumerable<T> according to a specified key selector function.
ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)

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

ToDictionary<TKey,TValue>(IEnumerable<ValueTuple<TKey,TValue>>, IEqualityComparer<TKey>)

Source:
ToCollection.cs
Source:
ToCollection.cs

Creates a dictionary from an enumeration according to specified key equality comparer.

public:
generic <typename TKey, typename TValue>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TValue> ^ ToDictionary(System::Collections::Generic::IEnumerable<ValueTuple<TKey, TValue>> ^ source, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.Dictionary<TKey,TValue> ToDictionary<TKey,TValue> (this System.Collections.Generic.IEnumerable<(TKey Key, TValue Value)> source, System.Collections.Generic.IEqualityComparer<TKey>? comparer);
static member ToDictionary : seq<ValueTuple<'Key, 'Value>> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Value>
<Extension()>
Public Function ToDictionary(Of TKey, TValue) (source As IEnumerable(Of ValueTuple(Of TKey, TValue)), comparer As IEqualityComparer(Of TKey)) As Dictionary(Of TKey, TValue)

Type Parameters

TKey

The type of the keys from elements of source.

TValue

The type of the values from elements of source.

Parameters

source
IEnumerable<ValueTuple<TKey,TValue>>

The enumeration to create a dictionary from.

comparer
IEqualityComparer<TKey>

An equality comparer to compare keys.

Returns

Dictionary<TKey,TValue>

A dictionary that contains keys and values from source.

Exceptions

ArgumentNullException

source is a null reference.

ArgumentException

source contains one or more duplicate keys.

Remarks

If comparer is null, the default equality comparer Default is used to compare keys.

Applies to

ToDictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>, IEqualityComparer<TKey>)

Source:
ToCollection.cs
Source:
ToCollection.cs

Creates a dictionary from an enumeration according to specified key comparer.

public:
generic <typename TKey, typename TValue>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TValue> ^ ToDictionary(System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>> ^ source, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.Dictionary<TKey,TValue> ToDictionary<TKey,TValue> (this System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>> source, System.Collections.Generic.IEqualityComparer<TKey>? comparer);
static member ToDictionary : seq<System.Collections.Generic.KeyValuePair<'Key, 'Value>> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Value>
<Extension()>
Public Function ToDictionary(Of TKey, TValue) (source As IEnumerable(Of KeyValuePair(Of TKey, TValue)), comparer As IEqualityComparer(Of TKey)) As Dictionary(Of TKey, TValue)

Type Parameters

TKey

The type of the keys from elements of source.

TValue

The type of the values from elements of source.

Parameters

source
IEnumerable<KeyValuePair<TKey,TValue>>

The enumeration to create a dictionary from.

comparer
IEqualityComparer<TKey>

An equality comparer to compare keys.

Returns

Dictionary<TKey,TValue>

A dictionary that contains keys and values from source.

Exceptions

ArgumentNullException

source is a null reference.

ArgumentException

source contains one or more duplicate keys.

Remarks

If comparer is null, the default equality comparer Default is used to compare keys.

Applies to

ToDictionary<TKey,TValue>(IEnumerable<KeyValuePair<TKey,TValue>>)

Source:
ToCollection.cs
Source:
ToCollection.cs

Creates a dictionary from an enumeration according to the default comparer for the key type.

public:
generic <typename TKey, typename TValue>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TValue> ^ ToDictionary(System::Collections::Generic::IEnumerable<System::Collections::Generic::KeyValuePair<TKey, TValue>> ^ source);
public static System.Collections.Generic.Dictionary<TKey,TValue> ToDictionary<TKey,TValue> (this System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<TKey,TValue>> source);
static member ToDictionary : seq<System.Collections.Generic.KeyValuePair<'Key, 'Value>> -> System.Collections.Generic.Dictionary<'Key, 'Value>
<Extension()>
Public Function ToDictionary(Of TKey, TValue) (source As IEnumerable(Of KeyValuePair(Of TKey, TValue))) As Dictionary(Of TKey, TValue)

Type Parameters

TKey

The type of the keys from elements of source.

TValue

The type of the values from elements of source.

Parameters

source
IEnumerable<KeyValuePair<TKey,TValue>>

The enumeration to create a dictionary from.

Returns

Dictionary<TKey,TValue>

A dictionary that contains keys and values from source and uses the default comparer for the key type.

Exceptions

ArgumentNullException

source is a null reference.

ArgumentException

source contains one or more duplicate keys.

Applies to

ToDictionary<TKey,TValue>(IEnumerable<ValueTuple<TKey,TValue>>)

Source:
ToCollection.cs
Source:
ToCollection.cs

Creates a dictionary from an enumeration according to the default comparer for the key type.

public:
generic <typename TKey, typename TValue>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TValue> ^ ToDictionary(System::Collections::Generic::IEnumerable<ValueTuple<TKey, TValue>> ^ source);
public static System.Collections.Generic.Dictionary<TKey,TValue> ToDictionary<TKey,TValue> (this System.Collections.Generic.IEnumerable<(TKey Key, TValue Value)> source);
static member ToDictionary : seq<ValueTuple<'Key, 'Value>> -> System.Collections.Generic.Dictionary<'Key, 'Value>
<Extension()>
Public Function ToDictionary(Of TKey, TValue) (source As IEnumerable(Of ValueTuple(Of TKey, TValue))) As Dictionary(Of TKey, TValue)

Type Parameters

TKey

The type of the keys from elements of source.

TValue

The type of the values from elements of source.

Parameters

source
IEnumerable<ValueTuple<TKey,TValue>>

The enumeration to create a dictionary from.

Returns

Dictionary<TKey,TValue>

A dictionary that contains keys and values from source and uses default comparer for the key type.

Exceptions

ArgumentNullException

source is a null reference.

ArgumentException

source contains one or more duplicate keys.

Applies to

ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)

Source:
ToCollection.cs
Source:
ToCollection.cs
Source:
ToCollection.cs

Creates a Dictionary<TKey,TValue> from an IEnumerable<T> according to specified key selector and element selector functions.

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TElement> ^ ToDictionary(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector);
public static System.Collections.Generic.Dictionary<TKey,TElement> ToDictionary<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector);
static member ToDictionary : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> -> System.Collections.Generic.Dictionary<'Key, 'Element>
<Extension()>
Public Function ToDictionary(Of TSource, TKey, TElement) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement)) As Dictionary(Of TKey, TElement)

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.

Parameters

source
IEnumerable<TSource>

An IEnumerable<T> to create a Dictionary<TKey,TValue> from.

keySelector
Func<TSource,TKey>

A function to extract a key from each element.

elementSelector
Func<TSource,TElement>

A transform function to produce a result element value from each element.

Returns

Dictionary<TKey,TElement>

A Dictionary<TKey,TValue> that contains values of type TElement selected from the input sequence.

Exceptions

ArgumentNullException

source or keySelector or elementSelector is null.

-or-

keySelector produces a key that is null.

ArgumentException

keySelector produces duplicate keys for two elements.

Remarks

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

Applies to

ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)

Source:
ToCollection.cs
Source:
ToCollection.cs
Source:
ToCollection.cs

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

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TElement> ^ ToDictionary(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.Dictionary<TKey,TElement> ToDictionary<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);
public static System.Collections.Generic.Dictionary<TKey,TElement> ToDictionary<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer);
static member ToDictionary : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Element>
<Extension()>
Public 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)

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.

Parameters

source
IEnumerable<TSource>

An IEnumerable<T> to create a Dictionary<TKey,TValue> from.

keySelector
Func<TSource,TKey>

A function to extract a key from each element.

elementSelector
Func<TSource,TElement>

A transform function to produce a result element value from each element.

comparer
IEqualityComparer<TKey>

An IEqualityComparer<T> to compare keys.

Returns

Dictionary<TKey,TElement>

A Dictionary<TKey,TValue> that contains values of type TElement selected from the input sequence.

Exceptions

ArgumentNullException

source or keySelector or elementSelector is null.

-or-

keySelector produces a key that is null.

ArgumentException

keySelector produces duplicate keys for two elements.

Remarks

If comparer is null, the default equality comparer Default is used to compare keys.

Applies to

ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)

Source:
ToCollection.cs
Source:
ToCollection.cs
Source:
ToCollection.cs

Creates a Dictionary<TKey,TValue> from an IEnumerable<T> according to a specified key selector function.

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TSource> ^ ToDictionary(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector);
public static System.Collections.Generic.Dictionary<TKey,TSource> ToDictionary<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector);
static member ToDictionary : seq<'Source> * Func<'Source, 'Key> -> System.Collections.Generic.Dictionary<'Key, 'Source>
<Extension()>
Public 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
IEnumerable<TSource>

An IEnumerable<T> to create a Dictionary<TKey,TValue> from.

keySelector
Func<TSource,TKey>

A function to extract a key from each element.

Returns

Dictionary<TKey,TSource>

A Dictionary<TKey,TValue> that contains keys and values. The values within each group are in the same order as in source.

Exceptions

ArgumentNullException

source or keySelector is null.

-or-

keySelector produces a key that is null.

ArgumentException

keySelector produces duplicate keys for two elements.

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.

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
    Console.WriteLine(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

Remarks

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

Applies to

ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)

Source:
ToCollection.cs
Source:
ToCollection.cs
Source:
ToCollection.cs

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

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::Dictionary<TKey, TSource> ^ ToDictionary(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.Dictionary<TKey,TSource> ToDictionary<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);
public static System.Collections.Generic.Dictionary<TKey,TSource> ToDictionary<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer);
static member ToDictionary : seq<'Source> * Func<'Source, 'Key> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Collections.Generic.Dictionary<'Key, 'Source>
<Extension()>
Public Function ToDictionary(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), comparer As IEqualityComparer(Of TKey)) As Dictionary(Of TKey, TSource)

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the keys returned by keySelector.

Parameters

source
IEnumerable<TSource>

An IEnumerable<T> to create a Dictionary<TKey,TValue> from.

keySelector
Func<TSource,TKey>

A function to extract a key from each element.

comparer
IEqualityComparer<TKey>

An IEqualityComparer<T> to compare keys.

Returns

Dictionary<TKey,TSource>

A Dictionary<TKey,TValue> that contains keys and values. The values within each group are in the same order as in source.

Exceptions

ArgumentNullException

source or keySelector is null.

-or-

keySelector produces a key that is null.

ArgumentException

keySelector produces duplicate keys for two elements.

Remarks

If comparer is null, the default equality comparer Default is used to compare keys.

Applies to