Lookup for each value in a delimited string

Hi Anonymous ，

Consider also using M for this:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjYxqTExM1WK1YlWMjQ2NQYzjI1NagzNzSzMITwLS6XYWAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Tester ID(s)" = _t]),
    #"Added Custom" = Table.AddColumn(Source, "ID", each Text.Split([#"Tester ID(s)"], "|")),
    #"Expanded ID" = Table.ExpandListColumn(#"Added Custom", "ID"),
    #"Changed Type1" = Table.TransformColumnTypes(#"Expanded ID", {{"ID", Int64.Type}}),
    #"Merged Queries" = Table.NestedJoin(#"Changed Type1", {"ID"}, UserInfoTable, {"ID"}, "UserInfoTable", JoinKind.LeftOuter),
    #"Expanded UserInfoTable" = Table.ExpandTableColumn(#"Merged Queries", "UserInfoTable", {"Name"}, {"Name"}),
    #"Grouped Rows" = Table.Group(#"Expanded UserInfoTable", {"Tester ID(s)"}, {{"Matched Tester Name(s)", each Text.Combine([Name], ",")}})
in
    #"Grouped Rows"

A sample file is attached for reference.

Best Regards,
Gao
Community Support Team

If there is any post helps, then please consider Accept it as the solution  to help the other members find it more quickly.
If I misunderstand your needs or you still have problems on it, please feel free to let us know. Thanks a lot!

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Hi Anonymous, different approach:

Result

let
    TestersTable = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjYxqTExM1WK1YlWMjQ2NQYzjI1NagzNzSzMITwLS6XYWAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Tester ID(s)" = _t]),
    UserInfoTable = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjY2UdJRcspPUorVAfJMQLyQzFwIz8ISyPPKTwXzTMxMgbzgUgjP0NzMwhykM7WkpFIpNhYA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [ID = _t, Name = _t]),
    BufferedUserInfo = Table.Buffer(UserInfoTable),
    Ad_MatchedTesterNames = Table.AddColumn(TestersTable, "Matched Tester Name(s)", each 
        [ a = Text.Split([#"Tester ID(s)"], "|"),
          b = List.Combine(List.Transform(a, (x)=> Table.SelectRows(BufferedUserInfo, (y)=> y[ID] = x)[Name])),
          c = if List.IsEmpty(b) then null else Text.Combine(b, ", ")
        ][c], type text)
in
    Ad_MatchedTesterNames