use List.Generate to create a conditional index gave me Expression.Error

[jimmyhua]

I tried to create a conditional index for another list I created. here is the code I wrote and error I got.  The first list is to create a position indicator where the index can began. The first one worked. and the second one gave the error.

=[
Splitposition= List.PositionOf(List.Transform(#"Filtered Rows"[Vendor Subline Num], each _ =1), true, Occurrence.All),

Conditionalindex = List.Generate(()=>0, each _ >= Splitposition, each _ +1)

]

Expression.Error: We cannot apply operator < to types List and Number.
Details:
Operator=<
Left=[List]
Right=0

[Omid_Motamedise]

the result of Splitposition is a list and
in this part

_ >= Splitposition

you can not compare a number (_) with a list (Splitposition).

you can replace it by _ >= Splitposition{0}

but if you explain the purpose of your function I can help you more

[lbendlin]

Occurrence.All will create a list.

[jimmyhua]

yes.  i do want a list because there are multiple 1s in the first list.  want i want to do is first to find the positions of the 1s then create fill in nulls in between each position so i can fill down and group them together.  is there a way to do it?

[lbendlin]

Please provide sample data that covers your issue or question completely, in a usable format (not as a screenshot).

Do not include sensitive information. Do not include anything that is unrelated to the issue or question.

Need help uploading data? https://community.fabric.microsoft.com/t5/Community-Blog/How-to-provide-sample-data-in-the-Power-BI-...

Please show the expected outcome based on the sample data you provided.

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[jimmyhua]

here is sample list1, which represents a column in a table that I need to group. each 1 starts a new group.  I use List.PositionOf to find out the positions where each group starts.  Then I want to fill in nulls and use fill down to fill the spaces.  I will use the new index column to group the entire table.
{1,1,2,3,1,2,1,2,3,4,5,1,2,3,1,1,2}

[slorin]

Hi @jimmyhua 

"here is sample list1, which represents a column in a table that I need to group. each 1 starts a new group."

You can use Table.Group directly

= Table.Group(
  YourSource,
  {"YourColumn"},
  {{"Data", each _}},
  GroupKind.Local,
  (x,y) => Byte.From(y[YourColumn]=1)
)

 Stéphane

[jimmyhua]

wow.  i have never used Table.Group function.  this is eye opening for me.  Thanks a lot.

[lbendlin]

Please show the expected outcome based on the sample data you provided.

[jimmyhua]

I would like to be able to create a list2 like this based on list1

{1,2,null,null,5,null,7,null,null,null,null,12,null,null,15,16,null}

[Omid_Motamedise · Accepted solution]

use the below formula

let
    Source = {1,1,2,3,1,2,1,2,3,4,5,1,2,3,1,1,2},
    Custom1 = List.Transform(List.Positions(Source), each if Source{_}=1 then _+1 else null)
in
    Custom1

result in 

[lbendlin]

let
    list1 = {1,1,2,3,1,2,1,2,3,4,5,1,2,3,1,1,2},
    list2 = List.Transform(List.Zip({list1,List.Positions(list1)}), each if _{0}=1 then _{1}+1 else null)
in
    list2