Adding a custom column to allow a filter in Table.profile

Not sure what you are getting at. A screenshot of a mockup would help. However, you can add custom aggregations to Table.Profile.

 

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclTSUTJUitWBsIzgLGMwywnIMoGzTOEsM6XYWAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Source = _t, Value = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Value", Int64.Type}}),
    Custom1 = 
        Table.Profile(
            #"Changed Type",
            { 
                {"Median", each Type.Is(_, type nullable number), List.Median},
                {"Mode", each Type.Is(_, type nullable number), List.Mode} 
            }
        )
in
    Custom1

 

Turns this:

into this

How to use M code provided in a blank query:
1) In Power Query, select New Source, then Blank Query
2) On the Home ribbon, select "Advanced Editor" button
3) Remove everything you see, then paste the M code I've given you in that box.
4) Press Done
5) See this article if you need help using this M code in your model.

 

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You could group your a, b, c, d, and then choose the All Rows aggregation. Then you could add a custom column with each Table.Profile(_[TableColumn]))

 

--Nate