Visual Basic.NET - Como calcular min de una columna segun grupo

Dim IDi As String

For DGV1 As Integer = 0 To DataGridView1.Rows.Count - 1

    IDi = DataGridView1.Item(0, DGV1).Value

    For DGV3 As Integer = 0 To DataGridView3.Rows.Count - 1

        If DataGridView3.Item(0, DGV3).Value = IDi Then

            Dim valorMaximo As Double = 0

            Dim valorMinimo As Double = Double.MaxValue

            For Each row As DataGridViewRow In DataGridView3.Rows

                If Not row.IsNewRow Then

                    If row.Cells(0).Value > valorMaximo Then

                        valorMaximo = row.Cells(0).Value

                    End If

                    If row.Cells(0).Value < valorMinimo Then

                        valorMinimo = row.Cells(0).Value

                    End If

                End If

            Next

            If DataGridView3.Item(1, DGV3).Value = valorMinimo Then

                DataGridView1.Item(1, DGV1).Value = DataGridView3.Item(1, DGV3).Value

            Else

            End If

        Else

        End If

    Next

Next

Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click

    Dim S As String

    Dim SPrecedente As String = ""

    Dim ValMin As Double

    Dim ValMax As Double

    ' **********

    ' Debemos ordenar el DVG con la coluna C0   ' !!! No necesario si es permide de cambiar DataGridView1

    ' Para no modificar DataGrdiView1, hacemos un duplica que volvemos cuando esta labor terminada

    Dim DGVTmp As New DataGridView()

    For C As Integer = 0 To DataGridView1.Columns.Count - 1

        DGVTmp.Columns.Add(DataGridView1.Columns(C).Clone)

    Next

    For R As Integer = 0 To DataGridView1.Rows.Count - 2 ' escribir -1 si  no ultima linea vacia en el DataGridView1

        DGVTmp.Rows.Add()

    Next

    For R As Integer = 0 To DataGridView1.Rows.Count - 2 ' escribir -1 si  no ultima linea vacia en el DataGridView1

        For C As Integer = 0 To DataGridView1.Columns.Count - 1

            DGVTmp.Item(C, R).Value = DataGridView1.Item(C, R).Value

        Next

    Next

    ' **********

    DataGridView1.Sort(DataGridView1.Columns("C0"), System.ComponentModel.ListSortDirection.Ascending)

    If DataGridView3.Rows.Count > 1 Then   ' escribir 0 si no ultima linea vacia en el DataGridView3

        DataGridView3.Rows.Clear()

    End If

' Aqui, este es el algoritmo para encontrar los Min y Max

    For R1 As Integer = 0 To DataGridView1.Rows.Count - 2  ' escribir -1 si  no ultima linea vacia en el DataGridView1

        S = DataGridView1.Item("C0", R1).Value

        If S = SPrecedente Then

            Continue For

        End If

        ValMin = DataGridView1.Item("C2", R1).Value

        ValMax = DataGridView1.Item("C2", R1).Value

        For R2 As Integer = R1 + 1 To DataGridView1.Rows.Count - 2  ' escribir -1 si  no ultima linea vacia en el DataGridView1

            If S = DataGridView1.Item("C0", R2).Value Then

                If ValMin > DataGridView1.Item("C2", R2).Value Then

                    ValMin = DataGridView1.Item("C2", R2).Value

                ElseIf ValMax < DataGridView1.Item("C2", R2).Value Then

                    ValMax = DataGridView1.Item("C2", R2).Value

                End If

            End If

        Next

        DataGridView3.Rows.Add(S, "Min", ValMin)   ' Aqui, registramos Min

        DataGridView3.Rows.Add(S, "Max", ValMax)  ' Aqui, registramos Max

        SPrecedente = S

    Next

    ' **********

    ' Debemos volver los datos iniciales de DataGridView1    ' !!! No necesario si DataGridView1 no registro precedamente

    For R As Integer = 0 To DataGridView1.Rows.Count - 2 ' escribir -1 si  no ultima linea vacia en el DataGridView1

        For C As Integer = 0 To DataGridView1.Columns.Count - 1

            DataGridView1.Item(C, R).Value = DGVTmp.Item(C, R).Value

        Next

    Next

    DGVTmp.Dispose()

    ' **********

End Sub