Power Query Custom Columns

Question

So, I am new to power query and I followed up a tutorial video on YouTube and tried to add a custom column so I can use it to see week over week improvements. Now, I have the inline PowerQuery to automate my weekly reporting. The problem here is that the added custom column is not named "Week". It is called the name of the file, instead. From this webpage the second parameter is the column name. I don't really understand why the column name is the filename instead of the name "week".

let ExcelFile = (FilePath, FileName) =>
let
    Source = Folder.Files(FilePath),
    File = Source{[#"Folder Path"=FilePath,Name=FileName]}[Content],
    ImportedExcel = Excel.Workbook(File),
    Sheet1 = ImportedExcel{[Name="Page1_1"]}[Data],
    TableWithWeek = Table.AddColumn(Sheet1,"Week", each FileName),
    TableWithoutHeader = Table.Skip(TableWithWeek,3),
    FirstRowAsHeader = Table.PromoteHeaders(TableWithoutHeader)
in
    FirstRowAsHeader
in
    ExcelFile

Answer 1

This call:

FirstRowAsHeader = Table.PromoteHeaders(TableWithoutHeader)

replaces the column names you have with the values from the first row. 

Since you have your first value under the column as the filename -"Week", your table is using that filename as the column name.

This can be fixed by adding the custom column after you use PromoteHeaders:

let ExcelFile = (FilePath, FileName) =>
    let
        Source = Folder.Files(FilePath),
        File = Source{[#"Folder Path"=FilePath,Name=FileName]}[Content],
        ImportedExcel = Excel.Workbook(File),
        Sheet1 = ImportedExcel{[Name="Page1_1"]}[Data],
        TableWithoutHeader = Table.Skip(Sheet1, 3),
        FirstRowAsHeader = Table.PromoteHeaders(TableWithoutHeader),
        TableWithWeek = Table.AddColumn(FirstRowAsHeader,"Week", each FileName),
    in
        TableWithWeek
in
    ExcelFile