主题：排除集合内重复值

如下代码

Vals = DataTables("air_shipment").GetValues("FOB_1_Currency|CIF_1_Currency|DDU_1_Currency", "[OriginCountry] is not null")
val.AddRange(vals)
Vals = DataTables("int_LCL").GetValues("FOB_1_Currency|CIF_1_Currency|DDU_1_Currency", "[Origin_Country] is not null")
val.AddRange(vals)
Vals = DataTables("international_FCL").GetValues("FOB_1_Currency|CIF_1_Currency|DDU_1_Currency", "[Origin_Country] is not null")
val.AddRange(vals)

以上为从各个表里面的数个列抓取不同的货币。
Dim Vals2 As new List(of String)
For i As Integer = 0 To Vals.Count - 1
    For u As Integer =0 To 2
        vals2.add(val(i)(u))
    Next
Next

以上为将字符数组的合并到一个集合里面，变成1维。

问题：如何排除掉vals2这个1维集合里面的重复的值？