Add suffix to column in Power Query if duplicates

[JoeCrozier]

Hello!

   I have data that looks like this:

I want to pivot it to look like this:

I.e. "completed date"'s become the values for the rows of protocol id's and columns of milestones.

As you can see, it pretty much works.  Problem is, every once and a while I have duplicates like this:

Where for a specific combination of protocol_id and milestone, I'll have two different dates.   I can clean up my data for now, but knowing the data source, it'll happen again.

So I was thinking one way to handle this might be to 'tag' them with indexes, maybe like this:

So that when I pivot it, I'll get a few more columns.  I may not use ALL of the columns, but at least I wont have errors.

I tried to follow this article to do so: https://excelguru.ca/label-duplicates-with-power-query/

but right when I got to the 

• Table.AddIndexColumn( [Data] , "Instance" , 1 )  step--- i started getting errors, specifically this one:
• 

I wonder if it has something to do with the way i grouped (by two variables).  Any ideas or suggestions?

[HotChilli · Accepted solution]

I think that's just telling you it doesn't know what [Data] is in that line.

Just from observation, it looks like the formula has been entered directly in the formula bar instead of in the Add Custom Column dialog.  I'm sure it will get wrapped with a reference to the previous query step if you do that.

[JoeCrozier]

Lol.  It was as simple as that, thank you.