calculate multiple filtered values from same column

Hello Anonymous 

in power query you can work with index-column and grouping. Here an example that shows you how to handle your puzzle

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSUUqKNzEAUobmQMLYyFQpVidayQhJ3BIkbmAAFgepT4s3BpKmIGxsBFcNETUCESYgQ2IB", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [week = _t, product_id = _t, stock = _t, sales = _t]),
    #"Sorted Rows" = Table.Sort(Source,{{"product_id", Order.Ascending},{"week", Order.Ascending}}),
    #"Changed Type" = Table.TransformColumnTypes(#"Sorted Rows",{{"week", Int64.Type}, {"product_id", type text}, {"stock", Int64.Type}, {"sales", Int64.Type}}),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 1, 1),
    #"Grouped Rows" = Table.Group
    (
        #"Added Index", 
        {"product_id"}, 
        {
            {
                "AllRows", 
                (tbl)=> Table.RemoveColumns(Table.AddColumn(tbl, "TotalBought", (add)=> let stockpreviousweek = try Table.SelectRows(tbl,  each [Index]= add[Index]-1)[stock]{0} otherwise 0 in add[stock]- stockpreviousweek + add[sales]), {"Index"})
            }
        }
    ),
    #"Expanded AllRows" = Table.ExpandTableColumn(#"Grouped Rows", "AllRows", {"week", "stock", "sales", "TotalBought"}, {"week", "stock", "sales", "TotalBought"})
in
    #"Expanded AllRows"

Copy paste this code to the advanced editor in a new blank query to see how the solution works.

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Kudoes are nice too

Have fun

Jimmy

Hi, Anonymous 

Based on your description, I created data to reproduce your scenario. The pbix file is attached in the end.

Table:

You may create a custom column with the following m codes.

let 
week = [Week],pid = [Product_id],
laststock = 
try
Table.SelectRows(#"Changed Type",each [Product_id]=pid and [Week]=week-1)[Stock]{0}
otherwise 
0
in 
[Sales]+[Stock]-laststock

Result:

Best Regards

Allan

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