Unpivot header

Hi everyone,

I have serveral csv files that I want to transform.

I want to create a function but I m unable to define how I can Unpivot all my files:

The first row contains period of time from column4 to ColumnX (it depends on the csv)

For each csv file, Periods could be different. In this screenshot I have 201401, 201402,... But sometimes I will have 201301,201203....

When in my function, i'm unpivoting The code is :

#"Changed Type1" = Table.TransformColumnTypes(#"Promoted Headers",{{"Column1", Int64.Type}, {"NoClient", Int64.Type}, {"NoProduit", Int64.Type}, {"Values", type text}, {"201401", type text}, {"201402", type text}, {"201403", type text}, {"201404", type text}, {"201405", type text}, {"201406", type text}, {"201407", type text}, {"201408", type text}, {"201409", type text}, {"201410", type text}, {"201411", type text}}),

#"Unpivoted Other Columns" = Table.UnpivotOtherColumns(#"Changed Type1", {"Column1", "NoClient", "NoProduit", "Values"}, "Attribute", "Value")

But when I want to use my function, I have this error : Expressio.error: the column 201401 of the table was not found.

Of course due to periods which are not the same...

I think the solution will be for me to add column 4 to x in the same colum (period) and transpose the column Type ?

Thanks for helping