Public Class frmCSV
 
    Dim WithEvents btn_In As New Button With _
        {.Parent = Me, .Text = "CSV-IN"}
 
    Dim WithEvents btn_out As New Button With _
        {.Parent = Me, .Text = "CSV_out", .Left = 150}
 
 
    Dim ofd As New OpenFileDialog, sfd As New SaveFileDialog
 
 
    Dim tboFilter As New TextBox With _
        {.Parent = Me, .Top = 50, .Width = 400}
 
    Dim dt As New DataTable, bs As New BindingSource
 
    Dim dgv As New DataGridView With {.Parent = Me, _
            .Top = 100, .Width = 400, .Height = 400, _
            .AllowUserToAddRows = False, .DataSource = bs}
 
    Dim FileName_In As String = "", filename_out As String = ""
 
 
 
    Private Sub frmCSV_Load(sender As System.Object, _
                            e As System.EventArgs) Handles MyBase.Load
 
        Me.Width = 420 : Me.Height = 550
 
        dt.Columns.Add("Spalte3") : dt.Columns.Add("Spalte5")
 
    End Sub
 
 
    Private Sub btn_In_Click(sender As Object, _
                             e As System.EventArgs) Handles btn_In.Click
 
        With ofd
            .Filter = "CSV|*csv"
            .CheckFileExists = True
            .Multiselect = False
            If .ShowDialog = _
                Windows.Forms.DialogResult.Cancel Then Exit Sub
 
            FileName_In = .FileName
 
            bs.DataSource = Nothing
            dt.Rows.Clear()
 
            Dim lines() As String = IO.File.ReadAllLines(.FileName)
            For i As Integer = 0 To lines.Length - 1
                Dim fields As New List(Of String)(lines(i).Split(";"c))
                If String.IsNullOrEmpty(tboFilter.Text) OrElse _
                    fields.Contains(tboFilter.Text) Then
                    If fields.Count >= 5 Then
                        dt.Rows.Add(fields(2), fields(4))
                    End If
                End If
            Next i
            bs.DataSource = dt
        End With
    End Sub
 
 
    Private Sub btn_out_Click(sender As Object, _
        e As System.EventArgs) Handles btn_out.Click
 
        Const linesperfile As Integer = 300 'max. Zeilen/Ausgabedatei
        Dim filecounter As Integer = 0
        Dim linecounter As Integer = 0
        Dim toOpen As Boolean = True
 
        With sfd
            .Filter = "CSV|*.csv"
            .DefaultExt = ".csv"
            If .ShowDialog = Windows.Forms.DialogResult.Cancel Then Exit Sub
            filename_out = .FileName.Substring(0, .FileName.Length - 4)
        End With
 
        Dim sr As IO.StreamWriter = Nothing
 
        If IO.File.Exists(FileName_In) Then
            For Each zeile As String In IO.File.ReadAllLines(FileName_In)
 
                Dim fields As New List(Of String)(zeile.Split(";"c))
                If String.IsNullOrEmpty(tboFilter.Text) OrElse _
                    fields.Contains(tboFilter.Text) Then
 
                    If toOpen Then
                        filecounter += 1
 
                        sr = New IO.StreamWriter(filename_out & "_" & _
                          filecounter.ToString & ".csv")
                        toOpen = False
                    End If
 
                    If fields.Count >= 5 Then
                        sr.WriteLine(fields(2) & ";" & fields(4))
                        linecounter += 1
 
                        If linecounter = linesperfile Then
                            sr.Close()
                            linecounter = 0
                            toopen = True
                        End If
                    End If
                End If
            Next zeile
            sr.Close()
        End If
    End Sub
End Class