Cumulative total that reset when is negative

Hi planc7 

You can try using the following method in PowerQuery.

let
  Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("TY/LDcAgDEN34QxSyKeUWRD7r9G4qmqO71mJk7WKipp5qSXKrh9G4vWjS6ITkXbiwKyQ7+Rmg2JCuP4isK91FkSHiEmhZ6MLciXqOz8pDBcdjHfyib0f", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Week = _t, Delta = _t]),
  #"Changed Type" = Table.TransformColumnTypes(
    Source,
    {{"Week", Int64.Type}, {"Delta", Int64.Type}}
  ),
  FX = (values as list) as list =>
    let
      GRTList = List.Generate(
        () => [GRT = values{0}, i = 0],
        each [i] < List.Count(values),
        each 
            let
                nextGRT = if [GRT] > 0 then [GRT] + values{[i] + 1} else values{[i] + 1}
            in
                [GRT = nextGRT, i = [i] + 1],
        each [GRT]
      )
    in
      GRTList,
  weeklist = List.Buffer(#"Changed Type"[Week]),
  deltalist = List.Buffer(#"Changed Type"[Delta]),
  result = Table.FromColumns(
    {Source[Week], Source[Delta], List.Transform(FX(deltalist), each if _ < 0 then 0 else _)},
    {"Week", "Delta", "Output"}
  ),
    #"Changed Type1" = Table.TransformColumnTypes(result,{{"Week", Int64.Type}, {"Delta", Int64.Type}, {"Output", Int64.Type}})
in
  #"Changed Type1"

Output:

Best Regards,
Yulia Xu

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