Dim groups As IEnumerable(Of IGrouping(Of String, FileInfo)) =
    New DirectoryInfo(".\").EnumerateFiles("*", SearchOption.TopDirectoryOnly).
                            GroupBy(Of String)(Function(file As FileInfo) file.Extension)
 
For Each group As IGrouping(Of String, FileInfo) In groups
 
    Dim sb As New StringBuilder(capacity:=(group.Count * 260)) ' Suggested capacity. 260 = MAX_PATH
    With sb
        .AppendFormat("Group of file extension '{0}'", group.Key)
        .AppendLine()
        .AppendLine(String.Join(Environment.NewLine, group))
    End With
    Console.WriteLine(sb.ToString())
 
Next group

Dim groups As IEnumerable(Of IGrouping(Of String, FileInfo)) =
    New DirectoryInfo(".\").EnumerateFiles("*", SearchOption.TopDirectoryOnly).
                            GroupBy(Of String)(Function(file As FileInfo) file.Extension)
 
Dim totalFileCount As Integer =
    groups.Sum(Function(group As IGrouping(Of String, FileInfo)) group.Count) ' Cantidad total de archivos.
 
For Each group As IGrouping(Of String, FileInfo) In groups
    Dim fileCount As Integer = group.Count ' Cantidad de archivos de este grupo.
    ...
Next group

        Dim groups As IEnumerable(Of IGrouping(Of String, FileInfo)) =
New DirectoryInfo(".\").EnumerateFiles("*", SearchOption.TopDirectoryOnly).
                     GroupBy(Of String)(Function(file As FileInfo) file.Extension)
        For Each group As IGrouping(Of String, FileInfo) In groups
            Dim sb As New StringBuilder(capacity:=(group.Count * 260)) ' Suggested capacity. 260 = MAX_PATH
            With sb
                .AppendFormat("'{0}'", group.Key)
                .AppendLine()
                .AppendLine(String.Join(Environment.NewLine, group))
            End With
            For Each Linea As String In sb.ToString
                TextBox1.Text += Linea
            Next
        Next group

 
        Dim DirInfo As New DirectoryInfo(".\")
        For Each Files As System.IO.FileInfo In DirInfo.GetFiles("*", SearchOption.TopDirectoryOnly)
            TextBox1.Text += String.Format("{0}{1}", Files.ToString, Environment.NewLine)
        Next