How to change several columns names using a formula?

[3xc3l]

I have a table in power query with several columns, among which are dates columns that follow the format YYYYDDMM##. I would like to rename all the dates columns using a formula, so that I change them for example to DD/MM/YYYY or MonYYYY (e.g. Jan2022). How can I do this? It is a huge number of columns, so doing it manually is not an option.

Thanks in advance for your help!

[edhans · Accepted solution]

Hi @3xc3l - this will do what you want.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WSlTSUTKE41idaKUkIMsIiI1BtBFYKBnINIEKmyjFxgIA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Test = _t, #"20210101" = _t, #"20210201" = _t, #"20210301" = _t]),
    ColumnNamesToList = Table.ColumnNames(Source),
    NewNames = 
        List.Transform(
            ColumnNamesToList, 
            each 
                if Text.Start(_,2) = "20" 
                then Text.End(_, 2) & "/" & Text.Middle(_, 4, 2) & "/" & Text.Start(_,4)
                else _
            ),
    CombinedLists = List.Zip({ColumnNamesToList,NewNames}),
    RenameColumns = Table.RenameColumns(Source, CombinedLists)
in
    RenameColumns

It turns this:

Into this fully dynamically. It looks for columns that start with a 20 assuming those are the years.

However, I am not convinced this is the best approach, but I don't know your data needs. Power BI will work MUCH better if that data is in a single column:
In my original data, I selected the TEST column and then Unpivot Other Columns.

Now just do normal data manipulation (like above with the Text.* functions) to convert that attribute to a date, the value types, then it doesn't matter if you have 2 columns or 200, all of your values are in one column and dates in another, and it will make your measures much easier.

How to use M code provided in a blank query:
1) In Power Query, select New Source, then Blank Query
2) On the Home ribbon, select "Advanced Editor" button
3) Remove everything you see, then paste the M code I've given you in that box.
4) Press Done
5) See this article if you need help using this M code in your model.

[jennratten]

Should the new column names be assigned incrementally, like Date1, Date2, Date3, etc?  Or do you have a list of the current names and what you'd like the new names to be?  There are a few different ways to handle this, but choosing which one will be based on the expected outcome.