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Grouping Data (Visual Basic)

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Grouping refers to the operation of putting data into groups so that the elements in each group share a common attribute.

The following illustration shows the results of grouping a sequence of characters. The key for each group is the character.

Diagram that shows a LINQ Grouping operation.

The standard query operator methods that group data elements are listed in the following section.

Methods

Method Name Description Visual Basic Query Expression Syntax More Information
GroupBy Groups elements that share a common attribute. Each group is represented by an IGrouping<TKey,TElement> object. Group … By … Into … Enumerable.GroupBy

Queryable.GroupBy
ToLookup Inserts elements into a Lookup<TKey,TElement> (a one-to-many dictionary) based on a key selector function. Not applicable. Enumerable.ToLookup

Query Expression Syntax Example

The following code example uses the Group By clause to group integers in a list according to whether they are even or odd.

Dim numbers As New System.Collections.Generic.List(Of Integer)(  
     New Integer() {35, 44, 200, 84, 3987, 4, 199, 329, 446, 208})  
  
Dim query = From number In numbers
            Group By Remainder = (number Mod 2) Into Group  
  
Dim sb As New System.Text.StringBuilder()  
For Each group In query  
    sb.AppendLine(If(group.Remainder = 0, vbCrLf & "Even numbers:", vbCrLf & "Odd numbers:"))  
    For Each num In group.Group  
        sb.AppendLine(num)  
    Next  
Next  
  
' Display the results.  
MsgBox(sb.ToString())  
  
' This code produces the following output:  
  
' Odd numbers:  
' 35  
' 3987  
' 199  
' 329  
  
' Even numbers:  
' 44  
' 200  
' 84  
' 4  
' 446  
' 208

See also