Dynamically Reference Calculated Row Above

[drewswiney]

Hello. I am looking to create column D of the table below in power query. You can see the excel formula to the right. I need to add columns from the current row and add a previously calculated row above.  I am stuck and do not know how to proceed. Any help would be appreciated.

	A	B	C	D
	Date	Production	Demand	Final Inventory	Formula in Column D
1	5/1/2021	80,287	96,419	158,276	N/A
2	6/1/2021	77,325	86,650	148,951	B3-C3+D2
3	7/1/2021	83,763	83,179	149,535	B4-C4+D3
4	8/1/2021	81,890	74,075	157,350	B5-C5+D4

[Vera_33 · Accepted solution]

Hi @drewswiney 

Add a helpColumn and an Index column

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("bY7JDYAwDARbQXmvhO3gI7Wg9EYtVEYAKZza1zxm7HlOpCPxKCSckNZl3xAECb+4GCYund8bWAPilipaz749d2TRW99gSo1Pw38+yHDLD2Yv3YgfgxGFbjcnkOth1A0=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, Production = _t, Demand = _t, Orignal = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}, {"Production", Int64.Type}, {"Demand", Int64.Type}, {"Orignal", Int64.Type}}),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "helpColumn", each if [Index]=0 then [Orignal] 
else [Production]- [Demand]),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Final Inventory", each List.Sum(List.FirstN(#"Added Custom"[helpColumn],[Index]+1)))
in
    #"Added Custom1"

[mahoneypat]

This calculation should probably be done on the DAX side with a measure or a column, but here is an example of how to do it in the query editor.  To see how it works, just create a blank query, open the Advanced Editor and replace the text there with the M code below.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("fY/JDcMwDARbMfhewKQkXrUI6i21pLI4fthOBAj7ms9gtnfSXfbCRQj0fn23BaOE35yGJnnx/zbRQHGjgU422dxRiz7sBlNe2FogVU6bz20VbvWHxVdtLaFVT1vMNkEkP1ob2HX19DhzxI/xAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, Production = _t, Demand = _t, #"Final Inventory" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}, {"Production", Int64.Type}, {"Demand", Int64.Type}, {"Final Inventory", Int64.Type}}),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),
    #"Added Custom" = Table.AddColumn(#"Added Index", "Custom", each if [Index] = 0 then null else [Production] - [Demand] + #"Changed Type"{[Index]-1}[Final Inventory], type number)
in
    #"Added Custom"

Pat