# Custom Grouping

Custom grouping is a flexible mechanism for creating groups by using  custom logic. It has a higher priority than the applied **GroupDescriptors** (added either by code or by dragging columns to the group panel).

Custom grouping is applied if user grouping is enabled through the **EnableGrouping** or **GridViewTemplate.EnableGrouping** properties. By default, grouping is enabled at all levels.

RadGridView provides two mechanisms for custom grouping:

* Handling the **CustomGrouping** event

* Replacing the RadGridView grouping mechanism by providing a custom **GroupPredicate**

You can use the **GroupSummaryEvaluate** event to format the group header row text of the created custom groups.

## Using the CustomGrouping event

The **CustomGrouping** event is fired if custom grouping is enabled through the **EnableCustomGrouping** or **GridViewTemplate.EnableCustomGrouping** properties. By default, custom grouping is disabled at all levels.

* **Template:** The template that holds the rows that will be grouped.

* **Row:** The row which group is defined.

* **Level:** The level of the current group, represents zero-based depth of the group.

* **GroupKey:** Identifier of the group.

* **Handled:** Defines whether the row is processed by the custom algorithm or by the applied group descriptors.

The following example demonstrates how to handle the **CustomGrouping** event to group  by the values of the `Country` column creating groups only for predefined countries:

> caption Figure 1 Custom Grouping

![WinForms RadGridView Custom Grouping](https://www.telerik.com/products/winforms/documentation/assets/c226f9174fb4a004408f7964dbddf7dd/gridview-grouping-custom-grouping001.png)

```C#
this.radGridView1.EnableCustomGrouping = true;
this.radGridView1.CustomGrouping += new GridViewCustomGroupingEventHandler(radGridView1_CustomGrouping);

GroupDescriptor descriptor = new GroupDescriptor("Country");
this.radGridView1.GroupDescriptors.Add(descriptor);

this.radGridView1.GroupSummaryEvaluate += new GroupSummaryEvaluateEventHandler(radGridView1_GroupSummaryEvaluate);
```

```VB.NET
Me.RadGridView1.EnableCustomGrouping = True

Dim descriptor As New GroupDescriptor("Country")
Me.RadGridView1.GroupDescriptors.Add(descriptor)
```

```C#
private void radGridView1_CustomGrouping(object sender, GridViewCustomGroupingEventArgs e)
{
    string country = e.Row.Cells["Country"].Value.ToString();
    switch (country)
    {
        case "USA":
            e.GroupKey = "1. USA";
            break;
        case "Japan":
            e.GroupKey = "2. Japan";
            break;
        case "Germany":
            e.GroupKey = "3. Germany";
            break;
        default:
            e.GroupKey = "Other country";
            break;
    }
}

private void radGridView1_GroupSummaryEvaluate(object sender, GroupSummaryEvaluationEventArgs e)
{
    if (e.Value == null)
    {
        e.FormatString = e.Group.Key.ToString();
    }
}
```

```VB.NET
Private Sub RadGridView1_CustomGrouping(ByVal sender As Object, ByVal e As Telerik.WinControls.UI.GridViewCustomGroupingEventArgs) Handles RadGridView1.CustomGrouping
    Dim country As String = e.Row.Cells("Country").Value.ToString()
    Select Case country
        Case "USA"
            e.GroupKey = "1. USA"
            Exit Select
        Case "Japan"
            e.GroupKey = "2. Japan"
            Exit Select
        Case "Germany"
            e.GroupKey = "3. Germany"
            Exit Select
        Case Else
            e.GroupKey = "Other country"
            Exit Select
    End Select
End Sub

Private Sub RadGridView1_GroupSummaryEvaluate(ByVal sender As Object, ByVal e As Telerik.WinControls.UI.GroupSummaryEvaluationEventArgs) Handles RadGridView1.GroupSummaryEvaluate
    If e.Value Is Nothing Then
        e.FormatString = e.Group.Key.ToString()
    End If
End Sub
```

When **RadGridView** is displaying date columns, it is a common requirement to perform grouping by certain part of the DateTime value. The example below will handle a scenario in which the date fields are grouped in year quarters.

> caption Figure: 2 DateTime Grouping Default Behavior

![WinForms RadGridView DateTime Grouping Default Behavior](https://www.telerik.com/products/winforms/documentation/assets/e51c7756c297b751c2a945973987930e/gridview-grouping-custom-grouping003.png)

> caption Figure: 3 DateTime Grouping Custom Behavior

![WinForms RadGridView DateTime Grouping Custom Behavior](https://www.telerik.com/products/winforms/documentation/assets/3a6c9edf18099b0944f928b35b770d71/gridview-grouping-custom-grouping004.png)

```C#
private void radGridView1_CustomGrouping(object sender, GridViewCustomGroupingEventArgs e)
{
    DateTime date = (DateTime)e.Row.Cells["Date"].Value;
    e.GroupKey = date.Year + " " + this.GetQuarter(date);
}

private string GetQuarter(DateTime date)
{
    if (date.Month >= 0 && date.Month <= 3)
    {
        return "Q1";
    }
    else if (date.Month >= 4 && date.Month <= 6)
    {
        return "Q2";
    }
    else if (date.Month >= 7 && date.Month <= 9)
    {
        return "Q3";
    }
    else
    {
        return "Q4";
    }
}

private void radGridView1_GroupSummaryEvaluate(object sender, GroupSummaryEvaluationEventArgs e)
{
    if (e.Value == null)
    {
        e.FormatString = e.Group.Key.ToString();
    }
}

```

```VB.NET
Private Sub radGridView1_CustomGrouping(sender As Object, e As GridViewCustomGroupingEventArgs)
    Dim [date] As DateTime = DirectCast(e.Row.Cells("Date").Value, DateTime)
    e.GroupKey = Convert.ToString([date].Year) & " " & Me.GetQuarter([date])
End Sub

Private Function GetQuarter([date] As DateTime) As String
    If [date].Month >= 0 AndAlso [date].Month <= 3 Then
        Return "Q1"
    ElseIf [date].Month >= 4 AndAlso [date].Month <= 6 Then
        Return "Q2"
    ElseIf [date].Month >= 7 AndAlso [date].Month <= 9 Then
        Return "Q3"
    Else
        Return "Q4"
    End If
End Function

Private Sub radGridView1_GroupSummaryEvaluate(sender As Object, e As GroupSummaryEvaluationEventArgs)
    If e.Value Is Nothing Then
        e.FormatString = e.Group.Key.ToString()
    End If
End Sub
```

## Implementing grouping mechanism by using GroupPredicate

You can replace the grouping mechanism in RadGridView with a custom one by setting the **GroupPredicate** of the **GridViewTemplate**.

The following example demonstrates how to use a custom grouping mechanism to group the rows by the values of the `ContactTitle` column, creating groups only for the desired contact title categories:

> caption Figure: 4 Implementing GroupPredicate

![WinForms RadGridView 4 Implementing GroupPredicate](https://www.telerik.com/products/winforms/documentation/assets/2521f69446ed447753497c69731326cc/gridview-grouping-custom-grouping002.png)

```C#

private object PerformGrouping(GridViewRowInfo row, int level)
{
    string title = row.Cells["ContactTitle"].Value.ToString();
    string groupKey;
    if (title.StartsWith("Sales"))
    {
        groupKey = "1. Sales contacts";
    }
    else if (title.StartsWith("Marketing"))
    {
        groupKey = "2. Marketing contacts";
    }
    else if (title.StartsWith("Accounting"))
    {
        groupKey = "3. Accounting contacts";
    }
    else
    {
        groupKey = "Other contacts";
    }
    return groupKey;
}
private void radGridView1_GroupSummaryEvaluate(object sender, GroupSummaryEvaluationEventArgs e)
{
    if (e.Value == null)
    {
        e.FormatString = e.Group.Key.ToString();
    }
}

```

```VB.NET

Private Function PerformGrouping(ByVal row As GridViewRowInfo, ByVal level As Integer) As Object
    Dim title As String = row.Cells("ContactTitle").Value.ToString()
    Dim groupKey As String
    If title.StartsWith("Sales") Then
        groupKey = "1. Sales contacts"
    ElseIf title.StartsWith("Marketing") Then
        groupKey = "2. Marketing contacts"
    ElseIf title.StartsWith("Accounting") Then
        groupKey = "3. Accounting contacts"
    Else
        groupKey = "Other contacts"
    End If
    Return groupKey
End Function
Private Sub RadGridView1_GroupSummaryEvaluate(ByVal sender As Object, ByVal e As Telerik.WinControls.UI.GroupSummaryEvaluationEventArgs) Handles RadGridView1.GroupSummaryEvaluate
    If e.Value Is Nothing Then
        e.FormatString = e.Group.Key.ToString()
    End If
End Sub

```

You can apply the predicate as it is demonstrated in the following code snippet:

```C#

GroupDescriptor descriptor = new GroupDescriptor("ContactTitle");
this.radGridView1.GroupDescriptors.Add(descriptor);

this.radGridView1.MasterTemplate.GroupPredicate = new GroupPredicate<GridViewRowInfo>(PerformGrouping);
this.radGridView1.GroupSummaryEvaluate += new GroupSummaryEvaluateEventHandler(radGridView1_GroupSummaryEvaluate);


```

```VB.NET

Dim descriptor As New GroupDescriptor("ContactTitle")
Me.RadGridView1.GroupDescriptors.Add(descriptor)
Me.RadGridView1.MasterTemplate.GroupPredicate = New GroupPredicate(Of GridViewRowInfo)(AddressOf PerformGrouping)


```

## See Also

* [Basic Grouping](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/basic-grouping)

* [Events](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/events)

* [Formatting Group Header Row](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/formatting-group-header-row)

* [Group Aggregates](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/group-aggregates)

* [Groups Collection](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/groups-collection)

* [Setting Groups Programmatically](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/setting-groups-programmatically)

* [Sorting group rows](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/sorting-group-rows)

* [Using Grouping Expressions](https://www.telerik.com/products/winforms/documentation/controls/gridview/features/grouping/using-grouping-expressions)