PowerBI: Power Query: Dealing with changing column names due to pivots - powerbi

Question

For a report I am making. I have a date column. I extract the months from that column and then pivot the months.
So for example I might have a table like:
Part#
Month
Qty
1
1
10
1
2
10
1
3
10
1
4
10
1
5
10
1
6
10
Which when I pivot it becomes:
Part#
1
2
3
4
5
6
1
10
10
10
10
10
10
I then rename the columns along with doing a few other tasks like creating a column of maximums.
However, since the data I pull is only for 6-months worth. These columns names will change.
In the future it may be:
Part#
4
5
6
7
8
9
1
10
10
10
10
10
10
So a line like:
Table.ReplaceValue(#"Pivoted Column",null,0,Replacer.ReplaceValue,{"1", "2", "3", "4", "5", "6"})
is going to create an error when the columns are 4,5,6,7,8,9. Is there a way to handle this issue?

Answer 1

You'll need to manually code a step to rename the columns after your pivot.
This M code pulls a table like the one in your example from the current workbook in Excel, then pivots as you describe, then renames the columns to Part#, 1st, 2nd, 3rd, 4th, 5th, and 6th. Yes, I said it renames to Part#, even though it doesn't really change that column name. Be sure to include Part# in the list coded in the step even though the Part# name isn't really changing, because you need to account for all column names extracted by Table.ColumnNames. Replace 1st, 2nd, 3rd, 4th, 5th, and 6th with your desired column names.
let
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
#"Pivoted Column" = Table.Pivot(Table.TransformColumnTypes(Source, {{"Month", type text}}, "en-US"), List.Distinct(Table.TransformColumnTypes(Source, {{"Month", type text}}, "en-US")[Month]), "Month", "Qty"),
#"Renamed Columns" = Table.RenameColumns(#"Pivoted Column", List.Zip({Table.ColumnNames(#"Pivoted Column"),{"Part#", "1st", "2nd", "3rd", "4th", "5th", "6th"}}))
in
#"Renamed Columns"
List.Zip interweaves two lists together. Here, it interweaves Part# from the original column names (those in the "Pivoted Column" step's table), then Part# from the list coded into #"Renamed Columns, then the next original column name (1 from your first example or 4 from your second example), then 1st from the column list coded into #"Renamed Columns, then the next original column name (2 from your first example or 5 from your second example), then 2nd from the column list coded into #"Renamed Columns, and so forth. This sets up the list needed for Table.RenameColumns.

Answer 2

You can use TableColumNames to get a list of column names, then you can transform that list. So for your example, you could use something like:
= Table.ReplaceValue(#"Pivoted Column",null,0,Replacer.ReplaceValue,List.Skip(Table.ColumnNames(#"Pivoted Column"),1))