Power Query Recursion: Simple reference of same row

PQ definitely support recursive functions. Your example does not contain any function though, so I do not understand your question.

FYI a recursive function: (the sign before the call of the function #"!" tells PQ it is a recursive call)

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Kees Stolker

A big fan of Power Query and Excel

This is the logic of the function:
AdjustedDate = 
If Table[Date] at index > Table[AdjustedDate] at index-1
then Table[Date] at index 
else Table[AdjustedDate] at index-1

Or in another fashion:
x = Table[Date] at index
y = Table[AdjustedDate] at index-1

 if x>y then x else y

If it were 2 columns A, B in excel it would be (starting at B2)
B2 = IF( B2>A1, B2, A1)

Ah! But in excel, every expression is evaluated on the level of a cell. In PowerQuery the expression is evaluated for the whole column (or table or whatever you pass it) at once.

In other words, Excel Formulas and M expressions work completely different.

And "at index" is not part of the syntax. You can refer to a row as {Index} but there is no concept of previous row in M.

My advice: Try to learn PowerQuery M language if you need heavy data crunching in excel, but never assume it to be similar to excel formula language in any way, even if there seem to be similarities.

Kees Stolker

A big fan of Power Query and Excel

Hi TuqueLogic, check this:

version with index (slower)

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlDSUTIyMDLVNzAEIqVYnWglQ2QhI7CQEZKQoQFYyBhZlQVYyARZlTFYyBRNKBYA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Index = _t, Date = _t]),
    ChangedType = Table.TransformColumnTypes(Source,{{"Index", Int64.Type}, {"Date", type date}}),
    Ad_AdjustedDate = Table.AddColumn(ChangedType, "Adjusted Date", each let a = try ChangedType{[Index]-1} otherwise [Date=[Date]] in if [Date] > a[Date] then [Date] else a[Date], type date)
in
    Ad_AdjustedDate

much faster version (index column is not needed)

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwMtU3MAQipVgdJK4RCtfQAFXWAlXWGIMbCwA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t]),
    ChangedType = Table.TransformColumnTypes(Source,{{"Date", type date}}),
    Ad_PevDate = Table.FromColumns(Table.ToColumns(ChangedType) & {{null} & List.RemoveLastN(ChangedType[Date], 1)}, Value.Type(Table.FirstN(ChangedType, 0) & #table(type table[PrevDate=date], {}))),
    Ad_AdjustedDate = Table.AddColumn(Ad_PevDate, "Adjusted Date", each if [Date] > ([PrevDate] ?? [Date]) then [Date] else ([PrevDate] ?? [Date]), type date),
    RemovedColumns = Table.RemoveColumns(Ad_AdjustedDate,{"PrevDate"})
in
    RemovedColumns

Hi TuqueLogic 

another solution with Table.Group and GroupKind.Local

let
Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwMtU3MAQipVgdJK4RCtfQAFXWAlXWGIMbCwA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t]),
ChangedType = Table.TransformColumnTypes(Source,{{"Date", type date}}),

Group = Table.Group(ChangedType, {"Date"}, {{"Data", each _}}, GroupKind.Local, (x,y)=> Byte.From(x[Date]<y[Date])),
Rename = Table.RenameColumns(Group,{{"Date", "AdjustedDate"}}),
Expand = Table.ExpandTableColumn(Rename, "Data", {"Date"}, {"Date"})
in
Expand

Stéphane 

I realize that using the Excel example confused the situation as I require being able to go back until a condtion is met, hence recursion.

This is the approximate form of the function DateRec()
= (x as number) as date =>
let
f=if ( DateTable{x}[Date] >= DateTable{x-1}[ImportDate] ) then DateTable{x}[Date] else DateRec(x-1)
in
if( x = 0) then DateTable{x}[Date] else f

But it is not letting me reference the column it is being used to create, DateTable[ImportDate].
Yet in the reference tutorial below, that is exactly what was done.

But the author chose the same column name as the function name so there is some abiguity in the functional relationships in the code and process.
(why the function and column were not called fibbFct and fibbCol or similar is beyond me)
https://radacad.com/fibonacci-sequence-understanding-the-power-query-recursive-function

Example of what the table should look like in the end below.
The first two columns are given, the ImportDate Column is the one to be created via the Invoke Custom Function:

Hi TuqueLogic,

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Hi TuqueLogic,

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Thank you.

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