Aggregation Operations

Artikel
02/04/2013

An aggregation operation computes a single value from a collection of values. An example of an aggregation operation is calculating the average daily temperature from a month's worth of daily temperature values.

The following illustration shows the results of two different aggregation operations on a sequence of numbers. The first operation sums the numbers. The second operation returns the maximum value in the sequence.

LINQ Aggregation Operations

The standard query operator methods that perform aggregation operations are listed in the following section.

Methods

Method Name	Description	C# Query Expression Syntax	Visual Basic Query Expression Syntax	More Information
Aggregate	Performs a custom aggregation operation on the values of a collection.	Not applicable.	Not applicable.	Enumerable.Aggregate Queryable.Aggregate
Average	Calculates the average value of a collection of values.	Not applicable.	Aggregate … In … Into Average()	Enumerable.Average Queryable.Average
Count	Counts the elements in a collection, optionally only those elements that satisfy a predicate function.	Not applicable.	Aggregate … In … Into Count()	Enumerable.Count Queryable.Count
LongCount	Counts the elements in a large collection, optionally only those elements that satisfy a predicate function.	Not applicable.	Aggregate … In … Into LongCount()	Enumerable.LongCount Queryable.LongCount
Max	Determines the maximum value in a collection.	Not applicable.	Aggregate … In … Into Max()	Enumerable.Max Queryable.Max
Min	Determines the minimum value in a collection.	Not applicable.	Aggregate … In … Into Min()	Enumerable.Min Queryable.Min
Sum	Calculates the sum of the values in a collection.	Not applicable.	Aggregate … In … Into Sum()	Enumerable.Sum Queryable.Sum

Query Expression Syntax Examples

Average

The following code example uses the Aggregate Into Average clause in Visual Basic to calculate the average temperature in an array of numbers that represent temperatures.


        Dim temperatures() As Double = {72.0, 81.5, 69.3, 88.6, 80.0, 68.5}

        Dim avg = Aggregate temp In temperatures Into Average()

        ' Display the result.
        MsgBox(avg)

        ' This code produces the following output:

        ' 76.65

Count

The following code example uses the Aggregate Into Count clause in Visual Basic to count the number of values in an array that are greater than or equal to 80.


        Dim temperatures() As Double = {72.0, 81.5, 69.3, 88.6, 80.0, 68.5}

        Dim highTemps As Integer = Aggregate temp In temperatures Into Count(temp >= 80)

        ' Display the result.
        MsgBox(highTemps)

        ' This code produces the following output:

        ' 3

LongCount

The following code example uses the Aggregate Into LongCount clause in Visual Basic to count the number of values in an array.


        Dim temperatures() As Double = {72.0, 81.5, 69.3, 88.6, 80.0, 68.5}

        Dim numTemps As Long = Aggregate temp In temperatures Into LongCount()

        ' Display the result.
        MsgBox(numTemps)

        ' This code produces the following output:

        ' 6

Max

The following code example uses the Aggregate Into Max clause in Visual Basic to calculate the maximum temperature in an array of numbers that represent temperatures.


        Dim temperatures() As Double = {72.0, 81.5, 69.3, 88.6, 80.0, 68.5}

        Dim maxTemp = Aggregate temp In temperatures Into Max()

        ' Display the result.
        MsgBox(maxTemp)

        ' This code produces the following output:

        ' 88.6

Min

The following code example uses the Aggregate Into Min clause in Visual Basic to calculate the minimum temperature in an array of numbers that represent temperatures.


        Dim temperatures() As Double = {72.0, 81.5, 69.3, 88.6, 80.0, 68.5}

        Dim minTemp = Aggregate temp In temperatures Into Min()

        ' Display the result.
        MsgBox(minTemp)

        ' This code produces the following output:

        ' 68.5

Sum

The following code example uses the Aggregate Into Sum clause in Visual Basic to calculate the total expense amount from an array of values that represent expenses.


        Dim expenses() As Double = {560.0, 300.0, 1080.5, 29.95, 64.75, 200.0}

        Dim totalExpense = Aggregate expense In expenses Into Sum()

        ' Display the result.
        MsgBox(totalExpense)

        ' This code produces the following output:

        ' 2235.2

Bagikan melalui

Aggregation Operations

Methods

Query Expression Syntax Examples

Average

Count

LongCount

Max

Min

Sum

See Also

Tasks

Reference

Concepts

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