Column accumulated by categories in power query

Hi CarlosOlmos29 

Here is a solution by using your formula. The logic is to group the table by category column and add an Index column to each group table first. Then add a column to each group table with your formula to get the running total within a group. Finally expand the group table column. 

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WSgQCJR0lQ6VYHfI4SUlJQLYR6exYAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Category = _t, Actual = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Category", type text}, {"Actual", Int64.Type}}),
    
    // add the following steps
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Category"}, {{"GroupData", each let actualValues = _[Actual] in Table.AddColumn(Table.AddIndexColumn(_, "Index", 1, 1), "RunningTotal", each List.Sum(List.Range(actualValues,0,[Index])))}}),
    #"Expanded GroupData" = Table.ExpandTableColumn(#"Grouped Rows", "GroupData", {"Actual", "Index", "RunningTotal"}, {"Actual", "Index", "RunningTotal"})
in
    #"Expanded GroupData"

PhilipTreacy 's blog link shares another solution. You can have a try!

Best Regards,
Jing
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