Hi there. Here's the M code that does exactly what you want. Please copy these queries and paste them right into the pane on the left (Queries). There are 2 functions in here, fnCumulativeSum and fnAddIndex and the main query/table, Products.
// fnCumulativeSum
(MyTable as table) as table =>
let
Source = Table.Buffer(MyTable),
TableType = Value.Type(Table.AddColumn(Source, "Running Sum", each null, type number)),
Cumulative = List.Skip(List.Accumulate(Source[Qty],{0},
(cumulative, cost) => cumulative & {List.Last(cumulative) + (if cost = null then 0 else cost)})
),
AddedRunningSum = Table.FromColumns(Table.ToColumns(Source)&{Cumulative},TableType)
in
AddedRunningSum
// fnAddIndex
(MyTable as table, StartIndex as number) as table =>
let
Source = Table.Buffer(MyTable),
AddIndex = Table.AddIndexColumn(Source, "Index", StartIndex, 1, Int64.Type)
in
AddIndex
// Products
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 [Month = _t, #"Product No." = _t, Qty = _t, #"Cumulative Qty" = _t, #"Test Identification [Desired Outcome]" = _t, #"Month with Production [Desired Outcome]" = _t]),
#"Removed Columns1" = Table.RemoveColumns(Source,{"Cumulative Qty", "Test Identification [Desired Outcome]", "Month with Production [Desired Outcome]"}),
#"Changed Type" = Table.TransformColumnTypes(#"Removed Columns1",{{"Month", type date}, {"Qty", Int64.Type}}),
#"Renamed Columns" = Table.RenameColumns(#"Changed Type",{{"Product No.", "ProdNo"}}),
#"Grouped Rows" = Table.Group(#"Renamed Columns", {"ProdNo"}, {{"CollapsedTable", each _, type table [Month=nullable date, ProdNo=nullable text, Qty=nullable number, CumulQty=nullable number, 10KTest=nullable text, MonthWithProd=nullable number]}}),
#"Invoked Custom Function" = Table.AddColumn(#"Grouped Rows", "CumulQtyTest", each fnCumulativeSum([CollapsedTable])),
#"Removed Columns" = Table.RemoveColumns(#"Invoked Custom Function",{"CollapsedTable"}),
#"Expanded CumulQtyTest" = Table.ExpandTableColumn(#"Removed Columns", "CumulQtyTest", {"Month", "ProdNo", "Qty", "Running Sum"}, {"Month", "ProdNo.1", "Qty", "Running Sum"}),
#"Removed Columns2" = Table.RemoveColumns(#"Expanded CumulQtyTest",{"ProdNo.1"}),
#"Renamed Columns1" = Table.RenameColumns(#"Removed Columns2",{{"Running Sum", "CumulQty"}}),
#"Added Custom" = Table.AddColumn(#"Renamed Columns1", "10KTest", each Number.IntegerDivide([CumulQty], 10000)),
#"Grouped Rows1" = Table.Group(#"Added Custom", {"ProdNo", "10KTest"}, {{"AllRows", each _, type table [ProdNo=nullable text, Month=date, Qty=nullable number, CumulQty=number, 10KTest=number]}, {"MinCumulQty", each List.Min([CumulQty]), type number}}),
#"Removed Columns3" = Table.RemoveColumns(#"Grouped Rows1",{"ProdNo", "10KTest"}),
#"Expanded AllRows" = Table.ExpandTableColumn(#"Removed Columns3", "AllRows", {"ProdNo", "Month", "Qty", "CumulQty", "10KTest"}, {"ProdNo", "Month", "Qty", "CumulQty", "10KTest"}),
#"Added Custom1" = Table.AddColumn(#"Expanded AllRows", "10KThresh", each if [MinCumulQty] = [CumulQty] and [10KTest] > 0 and [Qty] <> null then "10K Test" else ""),
#"Removed Columns4" = Table.RemoveColumns(#"Added Custom1",{"10KTest", "MinCumulQty"}),
#"Grouped Rows2" = Table.Group(#"Removed Columns4", {"ProdNo", "CumulQty"}, {{"AllRows", each _, type table [ProdNo=nullable text, Month=nullable date, Qty=nullable number, CumulQty=nullable number, 10KThresh=text]}}),
#"Grouped Rows3" = Table.Group(#"Grouped Rows2", {"ProdNo"}, {{"MinCumulOty", each List.Min([CumulQty]), type nullable number}, {"Rows", each _, type table [ProdNo=nullable text, CumulQty=nullable number, AllRows=table]}}),
#"Invoked Custom Function1" = Table.AddColumn(#"Grouped Rows3", "Index", each fnAddIndex([Rows], 1)),
#"Removed Columns5" = Table.RemoveColumns(#"Invoked Custom Function1",{"ProdNo", "Rows"}),
#"Expanded Index" = Table.ExpandTableColumn(#"Removed Columns5", "Index", {"ProdNo", "CumulQty", "AllRows", "Index"}, {"ProdNo", "CumulQty", "AllRows", "Index.1"}),
#"Added Custom2" = Table.AddColumn(#"Expanded Index", "Index.2", each if [MinCumulOty] = 0 then [Index.1] - 1 else [Index.1]),
#"Removed Columns6" = Table.RemoveColumns(#"Added Custom2",{"Index.1"}),
#"Replaced Value" = Table.ReplaceValue(#"Removed Columns6",0,null,Replacer.ReplaceValue,{"Index.2"}),
#"Added Custom3" = Table.AddColumn(#"Replaced Value", "MonthWithProd", each if [Index.2] <> 12 then Number.Mod([Index.2], 12) else 12),
#"Removed Columns7" = Table.RemoveColumns(#"Added Custom3",{"Index.2", "MinCumulOty", "ProdNo", "CumulQty"}),
#"Expanded AllRows1" = Table.ExpandTableColumn(#"Removed Columns7", "AllRows", {"ProdNo", "Month", "Qty", "CumulQty", "10KThresh"}, {"ProdNo", "Month", "Qty", "CumulQty", "10KThresh"})
in
#"Expanded AllRows1"
