Query Editor M new custom column: if statement that subtracts sum of other rows from one row

Hi alicek 

Download this sample PBIX file with the code below

This works for me

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclTSUTI0AAKlWJ1oJScoD8xxRua4wDmxAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Organization = _t, Amount = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Amount", Int64.Type}}),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "Custom", each if [Organization] = "A" then [Amount] - List.Sum(List.RemoveRange(Table.Column(#"Added Index", "Amount"),[Index],1)) else [Amount])
in
    #"Added Custom"

regards

Phil