直接上控制台代码：

Module Module1
    Sub Main()
        Console.WriteLine("请输入数据，以""，""相隔：")
        Dim str As String = Console.ReadLine

        Dim result = From x In str.Split(",")
                     Group By x Into Count
                     Where Count > 1
                     Select x

        Console.WriteLine("重复数据为：" & Join(result.Where(Function(x) x.ToString).ToArray, ","))
        Console.ReadKey()
    End Sub
End Module

演示效果：