Repeat same value in Power Query

[BICrazy]

Hi there Power BI Community,

I have this data set and would like to repeat the [DateMonth] value of [CollectionType] = "First" where the [CollectionType] = "Recurring".   I cannot use the fill-down function in this instance due to the layout of the data and am hoping to accomplish this in Power Query by adding a Custom Column.

My M code goes something along the lines of:  
Lines 1 and Line 3 are fine.  I need help to update line 2 please. so that the blanks in the custom column are replaced with the value of [DateMonth] that appears where Collection Type  = "First"

if [Collection Type]  = "First" then [DateMonth] 
else if [Collection Type] = "Recurring" then insert the record of [DateMonth] that is equal to "First"
else null

Here is an example of the dataset:

Here is an example of what the data set should end up looking like:

Thanks in advance.

[Fowmy · Accepted solution]

@BICrazy 

Add the following custom column : 

=
if [Collection Type] = "First" then
  [DateMonth]
else if [Collection Type] = "Recurring" then
  let
    m = _[DateMonth],
    p = _[#"Policy No#"]
  in
    Table.SelectRows(PreviousStep, each _[#"Policy No#"] = p and _[#"Collection Type"] = "First")[
      DateMonth
    ]{0}
else
  null

 Replace the "PreviousStep" with the correct step name in your query 

[BICrazy]

Hi @Fowmy ,

This is awesome, it worked perfectly! Thanks a mill