Group By Clause (Visual Basic)

Groups the elements of a query result. Can also be used to apply aggregate functions to each group. The grouping operation is based on one or more keys.

Group [ listField1 [, listField2 [...] ] By keyExp1 [, keyExp2 [...] ]
  Into aggregateList

Parts

Term	Definition
listField1, listField2	Optional. One or more fields of the query variable or variables that explicitly identify the fields to be included in the grouped result. If no fields are specified, all fields of the query variable or variables are included in the grouped result.
keyExp1	Required. An expression that identifies the key to use to determine the groups of elements. You can specify more than one key to specify a composite key.
keyExp2	Optional. One or more additional keys that are combined with keyExp1 to create a composite key.
aggregateList	Required. One or more expressions that identify how the groups are aggregated. To identify a member name for the grouped results, use the Group keyword, which can be in either of the following forms: Into Group -or- Into <alias> = Group You can also include aggregate functions to apply to the group.

Remarks

You can use the Group By clause to break the results of a query into groups. The grouping is based on a key or a composite key consisting of multiple keys. Elements that are associated with matching key values are included in the same group.

You use the aggregateList parameter of the Into clause and the Group keyword to identify the member name that is used to reference the group. You can also include aggregate functions in the Into clause to compute values for the grouped elements. For a list of standard aggregate functions, see Aggregate Clause (Visual Basic).

Example

The following code example groups a list of customers based on their location (country) and provides a count of the customers in each group. The results are ordered by country name. The grouped results are ordered by city name.

Public Sub GroupBySample()
  Dim customers = GetCustomerList()

  Dim customersByCountry = From cust In customers
                           Order By cust.City
                           Group By CountryName = cust.Country
                           Into RegionalCustomers = Group, Count()
                           Order By CountryName

  For Each country In customersByCountry
    Console.WriteLine(country.CountryName &
                      " (" & country.Count & ")" & vbCrLf)

    For Each customer In country.RegionalCustomers
      Console.WriteLine(vbTab & customer.CompanyName &
                        " (" & customer.City & ")")
    Next 
  Next 
End Sub

See Also

Reference

Select Clause (Visual Basic)

From Clause (Visual Basic)

Order By Clause (Visual Basic)

Aggregate Clause (Visual Basic)

Group Join Clause (Visual Basic)

Concepts

Introduction to LINQ in Visual Basic

Other Resources

Queries (Visual Basic)