Sumx with power query

Hello - yes, this can be done in Power Query.  Here is an example...

Goal: Add a column that contains the value of the current ListPrice column divided by the sum of the ListPrice column for all records with matching values in the Color, Size and Style columns.

BEFORE

AFTER

SCRIPT (comments are included that explain what's going on).

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("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", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Style = _t, Color = _t, Size = _t, ProductKey = _t, EnglishProductName = _t, ListPrice = _t]),
    ChangeType = Table.TransformColumnTypes(Source,{{"ProductKey", Int64.Type}, {"EnglishProductName", type text}, {"Color", type text}, {"ListPrice", type number}, {"Size", type text}}),
    Grouped = Table.Group(
        ChangeType, 
        {"Style", "Color", "Size"},                           // group rows by these columns
        {
            {"GroupedRows",                                   // name of the column with the grouped tables
                each                                          // current iteration of the table...
                let                                           // create some variables
                    varTable = Table.Buffer ( _ ),            // read the current nested table into memory
                    varSum = List.Sum([ListPrice])            // denominator 
                in  
                    Table.AddColumn (                         // add a new column
                        varTable,                             // to the grouped table
                        "Calculation",                        // new column name
                        each Value.Divide (                   // new column value
                            Record.Field ( _, "ListPrice" ),  // current row of the nested table
                            varSum                            // sum of grouped value
                        ),
                        type table
                    )
            }
        }
    ),
    // Expand all columns in the nested tables that are not present in the Grouped table. 
    expand = Table.ExpandTableColumn (
        Grouped,
        "GroupedRows", 
        List.Difference ( 
            Table.ColumnNames ( Table.Combine ( Grouped[GroupedRows] ) ),
            Table.ColumnNames ( Grouped )
        )
    ),
    #"Sorted Rows" = Table.Sort(expand,{{"ProductKey", Order.Ascending}}),
    #"Changed Type" = Table.TransformColumnTypes(#"Sorted Rows",{{"ProductKey", Int64.Type}, {"EnglishProductName", type text}, {"ListPrice", Currency.Type}, {"Calculation", Percentage.Type}})
in
    #"Changed Type"