How to sum consecutive rows in Power Query - sum

Question

I have in Power Query a Column "% sum of all". I need to create a custom column "Sum Consecutive" that each row has as value the "% sum of all" of the current row + the value of "Sum Consecutive" of the previous row.
Current row situation
New Custom Column Expectation
You can see two images that show the current situation and the next situation I need in the Power Query.
Can you please help me find a code/command to create this new column like that?
Although there are similar solved questions in DAX, I still need to keep editing the file after that, so it should be performed in M language in power query.
Thank you!

Answer 1

Not sure how performant my approaches are. I would think both should be reasonably efficient as they only loop over each row in the table once (and "remember" the work done in the previous rows). However, maybe the conversion to records/list and then back to table is slow for large tables (I don't know).
Approach 1: Isolate the input column as a list, transform the list by cumulatively adding, put the transformed list back in the table as a new column.
let
someTable = Table.FromColumns({List.Repeat({0.0093}, 7) & List.Repeat({0.0086}, 7) & {0.0068, 0.0068}}, {"% of sum of all"}),
listToLoopOver = someTable[#"% of sum of all"],
cumulativeSum = List.Accumulate(List.Positions(listToLoopOver), {}, (listState, currentIndex) =>
let
numberToAdd = listToLoopOver{currentIndex},
sum = try listState{currentIndex - 1} + numberToAdd otherwise numberToAdd,
append = listState & {sum}
in
append
),
backToTable = Table.FromColumns(Table.ToColumns(someTable) & {cumulativeSum}, Table.ColumnNames(someTable) & {"Cumulative sum"})
in
backToTable
Approach 2: Convert the table to a list of records, loop over each record and add a new field (representing the new column) to each record, then convert the transformed list of records back into a table.
let
someTable = Table.FromColumns({List.Repeat({0.0093}, 7) & List.Repeat({0.0086}, 7) & {0.0068, 0.0068}}, {"% of sum of all"}),
listToLoopOver = Table.ToRecords(someTable),
cumulativeSum = List.Accumulate(List.Positions(listToLoopOver), {}, (listState, currentIndex) =>
let
numberToAdd = Record.Field(listToLoopOver{currentIndex}, "% of sum of all"),
sum = try listState{currentIndex - 1}[Cumulative sum] + numberToAdd otherwise numberToAdd, // 'try' should only be necessary for first item
recordToAdd = listToLoopOver{currentIndex} & [Cumulative sum = sum],
append = listState & {recordToAdd}
in
append
),
backToTable = Table.FromRecords(cumulativeSum)
in
backToTable
I couldn't find a function in the reference for M/Power Query that sums a list cumulatively.