Enumerable.ToDictionary 方法
定义
从 IEnumerable<T> 创建一个 Dictionary<TKey,TValue>。Creates a Dictionary<TKey,TValue> from an IEnumerable<T>.
重载
ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)
根据指定的键选择器和元素选择器函数,从 IEnumerable<T> 创建一个 Dictionary<TKey,TValue>。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)
类型参数
- TSource
source 的元素类型。The type of the elements of source.
- TKey
keySelector 返回的键的类型。The type of the key returned by keySelector.
- TElement
elementSelector 返回的值的类型。The type of the value returned by elementSelector.
参数
- source
- IEnumerable<TSource>
要从其创建 Dictionary<TKey,TValue> 的 IEnumerable<T>。An IEnumerable<T> to create a Dictionary<TKey,TValue> from.
- keySelector
- Func<TSource,TKey>
用于从每个元素中提取键的函数。A function to extract a key from each element.
- elementSelector
- Func<TSource,TElement>
用于从每个元素产生结果元素值的转换函数。A transform function to produce a result element value from each element.
返回
- Dictionary<TKey,TElement>
一个包含从输入序列中选择的类型为 TElement 的值的 Dictionary<TKey,TValue>。A Dictionary<TKey,TValue> that contains values of type TElement selected from the input sequence.
例外
source、keySelector 或 elementSelector 为 null。source or keySelector or elementSelector is null.
- 或 --or-
keySelector 生成一个 null 的键。keySelector produces a key that is null.
keySelector 为两个元素生成重复键。keySelector produces duplicate keys for two elements.
注解
ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)方法使用默认的相等比较器 Default 对键进行比较。The ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) method uses the default equality comparer Default to compare keys.
适用于
ToDictionary<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)
根据指定的键选择器函数、比较器和元素选择器函数,从 IEnumerable<T> 创建一个 Dictionary<TKey,TValue>。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)
类型参数
- TSource
source 的元素类型。The type of the elements of source.
- TKey
keySelector 返回的键的类型。The type of the key returned by keySelector.
- TElement
elementSelector 返回的值的类型。The type of the value returned by elementSelector.
参数
- source
- IEnumerable<TSource>
要从其创建 Dictionary<TKey,TValue> 的 IEnumerable<T>。An IEnumerable<T> to create a Dictionary<TKey,TValue> from.
- keySelector
- Func<TSource,TKey>
用于从每个元素中提取键的函数。A function to extract a key from each element.
- elementSelector
- Func<TSource,TElement>
用于从每个元素产生结果元素值的转换函数。A transform function to produce a result element value from each element.
- comparer
- IEqualityComparer<TKey>
用于比较键的 IEqualityComparer<T>。An IEqualityComparer<T> to compare keys.
返回
- Dictionary<TKey,TElement>
一个包含从输入序列中选择的类型为 TElement 的值的 Dictionary<TKey,TValue>。A Dictionary<TKey,TValue> that contains values of type TElement selected from the input sequence.
例外
source、keySelector 或 elementSelector 为 null。source or keySelector or elementSelector is null.
- 或 --or-
keySelector 生成一个 null 的键。keySelector produces a key that is null.
keySelector 为两个元素生成重复键。keySelector produces duplicate keys for two elements.
注解
如果 comparer 为 null ,则使用默认的相等比较器 Default 对键进行比较。If comparer is null, the default equality comparer Default is used to compare keys.
适用于
ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)
根据指定的键选择器函数,从 IEnumerable<T> 创建一个 Dictionary<TKey,TValue>。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)
类型参数
- TSource
source 的元素类型。The type of the elements of source.
- TKey
keySelector 返回的键的类型。The type of the key returned by keySelector.
参数
- source
- IEnumerable<TSource>
要从其创建 Dictionary<TKey,TValue> 的 IEnumerable<T>。An IEnumerable<T> to create a Dictionary<TKey,TValue> from.
- keySelector
- Func<TSource,TKey>
用于从每个元素中提取键的函数。A function to extract a key from each element.
返回
- Dictionary<TKey,TSource>
一个包含键和值的 Dictionary<TKey,TValue>。A Dictionary<TKey,TValue> that contains keys and values. 每个组中的值顺序与 source 中的顺序相同。The values within each group are in the same order as in source.
例外
source 或 keySelector 为 null。source or keySelector is null.
- 或 --or-
keySelector 生成一个 null 的键。keySelector produces a key that is null.
keySelector 为两个元素生成重复键。keySelector produces duplicate keys for two elements.
示例
下面的代码示例演示如何使用 ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) Dictionary<TKey,TValue> 通过键选择器创建。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
注解
ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)方法使用默认的相等比较器 Default 对键进行比较。The ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) method uses the default equality comparer Default to compare keys.
适用于
ToDictionary<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)
根据指定的键选择器函数和键比较器,从 IEnumerable<T> 创建一个 Dictionary<TKey,TValue>。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)
类型参数
- TSource
source 的元素类型。The type of the elements of source.
- TKey
keySelector 返回的键的类型。The type of the keys returned by keySelector.
参数
- source
- IEnumerable<TSource>
要从其创建 Dictionary<TKey,TValue> 的 IEnumerable<T>。An IEnumerable<T> to create a Dictionary<TKey,TValue> from.
- keySelector
- Func<TSource,TKey>
用于从每个元素中提取键的函数。A function to extract a key from each element.
- comparer
- IEqualityComparer<TKey>
用于比较键的 IEqualityComparer<T>。An IEqualityComparer<T> to compare keys.
返回
- Dictionary<TKey,TSource>
一个包含键和值的 Dictionary<TKey,TValue>。A Dictionary<TKey,TValue> that contains keys and values. 每个组中的值顺序与 source 中的顺序相同。The values within each group are in the same order as in source.
例外
source 或 keySelector 为 null。source or keySelector is null.
- 或 --or-
keySelector 生成一个 null 的键。keySelector produces a key that is null.
keySelector 为两个元素生成重复键。keySelector produces duplicate keys for two elements.
注解
如果 comparer 为 null ,则使用默认的相等比较器 Default 对键进行比较。If comparer is null, the default equality comparer Default is used to compare keys.