How to sum N columns in Power Query - excel

Question

My data gets updated every month so I'm trying to create a power query table that would show the sum of the pivoted (N) columns that I created but I can't seem to figure out how to do it in power query.
I have this code currently:

Answer 1

After Pivoting:
Create a list of the columns to sum
Add an Index column to restrict to each row
Add a column which Sums the columns for just that row
Remove the Index colum
let
Source = Excel.CurrentWorkbook(){[Name="Table3"]}[Content],
#"Changed Type" = Table.TransformColumnTypes(Source,{{"Month Yr", Date.Type}, {"Attribute", type text}, {"Value", Currency.Type}}),
#"Added Custom" = Table.AddColumn(#"Changed Type", "MonthYear", each Date.ToText([Month Yr],"MMMM yyyy")),
#"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"Month Yr"}),
#"Pivoted Column" = Table.Pivot(#"Removed Columns", List.Distinct(#"Removed Columns"[MonthYear]), "MonthYear", "Value", List.Sum),
//NEW code added after your Pivoted Column line
//Get List of columns to sum
// Assumes this list all columns **except the first** in the Pivot table
// There are other methods of generating this list if this assumption is incorrect
colToSum = List.RemoveFirstN(Table.ColumnNames(#"Pivoted Column"),1),
//Add Index Column
IDX = Table.AddIndexColumn(#"Pivoted Column","Index",0,1),
//Sum each row of "colToSum"
totals = Table.AddColumn(IDX, "Sum", each List.Sum(
Record.ToList(
Table.SelectColumns(IDX,colToSum){[Index]})
), Currency.Type),
#"Removed Columns1" = Table.RemoveColumns(totals,{"Index"})
in
#"Removed Columns1"

Answer 2

You can group and then merge into the table after pivoting
#"Grouped Rows" = Table.Group(#"Changed Type", {"Atribute"}, {{"Sum", each List.Sum([Value]), type number}}),
#"Pivoted Column" = Table.Pivot(Table.TransformColumnTypes(#"Changed Type", {{"Month Year", type text}}, "en-US"), List.Distinct(Table.TransformColumnTypes(#"Changed Type", {{"Month Year", type text}}, "en-US")[#"Month Year"]), "Month Year", "Value", List.Sum),
#"Merged Queries" = Table.NestedJoin(#"Pivoted Column",{"Atribute"}, #"Grouped Rows",{"Atribute"},"Table2",JoinKind.LeftOuter),
#"Expanded Table" = Table.ExpandTableColumn(#"Merged Queries", "Table2", {"Sum"}, {"Sum"})
in #"Expanded Table"
Or you can group, add it to the table, then pivot the combined new set
#"Grouped Rows" = Table.Group(#"Changed Type", {"Atribute"}, {{"Value", each List.Sum([Value]), type number}}),
#"Added Custom" = Table.AddColumn(#"Grouped Rows", "Month Year", each "Sum"),
#"Reordered Columns" = Table.ReorderColumns(#"Added Custom",{"Month Year", "Atribute", "Value"}),
combined = #"Reordered Columns" & #"Changed Type",
#"Pivoted Column" = Table.Pivot(Table.TransformColumnTypes(combined, {{"Month Year", type text}}, "en-US"), List.Distinct(Table.TransformColumnTypes(combined, {{"Month Year", type text}}, "en-US")[#"Month Year"]), "Month Year", "Value", List.Sum)
in #"Pivoted Column"