Статья
11/17/2011

Enumerable.Aggregate<TSource, TAccumulate, TResult> Method (IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>)

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Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Aggregate(Of TSource, TAccumulate, TResult) ( _
    source As IEnumerable(Of TSource), _
    seed As TAccumulate, _
    func As Func(Of TAccumulate, TSource, TAccumulate), _
    resultSelector As Func(Of TAccumulate, TResult) _
) As TResult

public static TResult Aggregate<TSource, TAccumulate, TResult>(
    this IEnumerable<TSource> source,
    TAccumulate seed,
    Func<TAccumulate, TSource, TAccumulate> func,
    Func<TAccumulate, TResult> resultSelector
)

Type Parameters

TSource
The type of the elements of source.

TAccumulate
The type of the accumulator value.

TResult
The type of the resulting value.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> to aggregate over.

seed
Type: TAccumulate
The initial accumulator value.

func
Type: System.Func<TAccumulate, TSource, TAccumulate>
An accumulator function to be invoked on each element.

resultSelector
Type: System.Func<TAccumulate, TResult>
A function to transform the final accumulator value into the result value.

Return Value

Type: TResult
The transformed final accumulator value.

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 func or resultSelector is nulla null reference (Nothing in Visual Basic).

Remarks

The Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>) method makes it simple to perform a calculation over a sequence of values. This method works by calling func one time for each element in source. Each time func is called, Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>) passes both the element from the sequence and an aggregated value (as the first argument to func). The value of the seed parameter is used as the initial aggregate value. The result of func replaces the previous aggregated value. The final result of func is passed to resultSelector to obtain the final result of Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>).

To simplify common aggregation operations, the standard query operators also include a general purpose count method, Count, and four numeric aggregation methods, namely Min, Max, Sum, and Average.

Examples

The following code example demonstrates how to use Aggregate to apply an accumulator function and a result selector.

   Sub AggregateEx3()
      Dim fruits() As String = _
          {"apple", "mango", "orange", "passionfruit", "grape"}

      ' Determine whether any string in the array is longer than "banana".
      Dim longestName As String = _
          fruits.Aggregate("banana", _
                           Function(longest, fruit) _
                               IIf(fruit.Length > longest.Length, fruit, longest), _
                           Function(fruit) fruit.ToUpper())

      ' Display the output.
      outputBlock.Text &= "The fruit with the longest name is " & longestName & vbCrLf
   End Sub

   ' This code produces the following output:
   '
   ' The fruit with the longest name is PASSIONFRUIT

      string[] fruits = { "apple", "mango", "orange", "passionfruit", "grape" };

      // Determine whether any string in the array is longer than "banana".
      string longestName =
          fruits.Aggregate("banana",
                          (longest, next) =>
                              next.Length > longest.Length ? next : longest,
         // Return the final result as an upper case string.
                          fruit => fruit.ToUpper());

      outputBlock.Text += String.Format(
          "The fruit with the longest name is {0}.",
          longestName) + "\n";

      // This code produces the following output:
      //
      // The fruit with the longest name is PASSIONFRUIT.

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.

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