How to fill up / fill down in power query , grouped by another column

Question

Suppose I have this table

Customer No	Ending Balance
C001	NULL
C001	100
C001	NULL
C002	NULL
C002	NULL
C002	499
C002	NULL
C002	599
C002	NULL

And I want this result

Customer No	Ending Balance
C001	100
C001	100
C001	100
C002	499
C002	499
C002	499
C002	499
C002	599
C002	599

I was think to use fill down and fill up, after the fill down, I get this

Customer No	Ending Balance
C001	100
C001	100
C001	100
C002	100 (Wrong)
C002	100 (Wrong)
C002	499
C002	499
C002	599
C002	599

Is there a way to use fill down / fill up based on a group column?

Answer 1

Here you go.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WcjYwMFRQ0lHyC/XxUYrVQQgYGhig8JEVGBEnYGJpiV+BKVYFsQA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Customer No" = _t, #"Ending Balance" = _t]),
    #"Replaced Value" = Table.ReplaceValue(Source,"NULL",null,Replacer.ReplaceValue,{"Ending Balance"}),
    #"Changed Type" = Table.TransformColumnTypes(#"Replaced Value",{{"Customer No", type text}, {"Ending Balance", type text}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Customer No"}, {{"All", each _, type table [Customer No=nullable text, Ending Balance=nullable text]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Custom", each Table.FillUp( Table.FillDown([All], {"Ending Balance"}), {"Ending Balance"})),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"All"}),
    #"Expanded Custom" = Table.ExpandTableColumn(#"Removed Columns", "Custom", {"Ending Balance"}, {"Ending Balance"})
in
    #"Expanded Custom"

Steps

Group your table as follows:

Add a custom column as follows:

Expand and remove redundant columns and voila.