PowerQuery：如何從同一Excel工作表中單獨列中的文件夾中導入多個文本文件

Question

我想從一個文件夾中導入多個文本文件，每個文件包含兩列，將它們導入到一個Excel工作表中，以便每個新文件都從一個新列開始。 理想情況下，我需要第一個文件中的兩列，而每個其他文本文件中只需要第二列。 在powerquery中，我嘗試使用“從文件夾導入（導入元數據和有關文件夾中文件的鏈接）”功能，然后使用查詢編輯器並展開二進制文件，結果是每個新文件都附加在上一個文件的末尾。 但是我希望每個文件都在同一張紙中開始一個新列，但我不知道該怎么做。

我該如何指示powerquery做到這一點？ 在此先感謝您的幫助！

Answer 1

我的建議包括通過高級編輯器添加的2個相當困難的步驟，但是對於文件夾中.txt文件的數量，它是動態的。 我添加了很多評論，所以應該可以自我解釋。

/*  In this query, .txt files from a folder are combined.
Each source file has 2 columns.
The resulting table consists of both columns from the first file and each second column from the other files.
Tables are joined using each first column as key and with a left outer join
It is assumed that each file has column headers in the first row, that the first column header is the same for each file
    and, preferably, the second column header differs per file, although this is not necessary.
This query is tested with the following file contents:

File1.txt:
    ID,File1
    1,A
    2,B
    3,C
    4,D

File2.txt:
    ID,File2
    1,W
    2,X
    3,Y

Another file was added later on, to test for .txt files being added to the folder: works fine!
*/    

let
// Standard UI:
Source = Folder.Files("C:\Users\Marcel\Documents\Forum bijdragen\StackOverflow Power Query\Multiple files in 1 folder"),

// Standard UI; step renamed
FilteredTxt = Table.SelectRows(Source, each [Extension] = ".txt"),

// Standard UI; step renamed
RemovedColumns = Table.RemoveColumns(FilteredTxt,{"Name", "Extension", "Date accessed", "Date modified", "Date created", "Attributes", "Folder Path"}),

// UI add custom column "FileContents" with formula Csv.Document([Content]); step renamed
AddedFileContents = Table.AddColumn(RemovedColumns, "FileContents", each Csv.Document([Content])),

// Standard UI; step renamed
RemovedBinaryContent = Table.RemoveColumns(AddedFileContents,{"Content"}),

// In the next 3 steps, temporary names for the new columns are created ("Column2", "Column3", etcetera)
// Standard UI: add custom Index column, start at 2, increment 1
#"Added Index" = Table.AddIndexColumn(RemovedBinaryContent, "Index", 2, 1),

// Standard UI: select Index column, Transform tab, Format, Add Prefix: "Column"
#"Added Prefix" = Table.TransformColumns(#"Added Index", {{"Index", each "Column" & Text.From(_, "en-US"), type text}}),

// Standard UI:
#"Renamed Columns" = Table.RenameColumns(#"Added Prefix",{{"Index", "ColumnName"}}),
// Now we have the names for the new columns

// Advanced Editor: create a list with records with FileContents (tables) and ColumnNames (text) (1 list item (or record) per txt file in the folder)
// From this list, the resulting table will be build in the next step.
ListOfRecords = Table.ToRecords(#"Renamed Columns"),

// Advanced Editor: use List.Accumulate to build the table with all columns, 
// starting with Column1 of the first file (Table.FromList(ListOfRecords{0}[FileContents][Column1], each {_}),)
// adding Column2 of each file for all items in ListOfRecords.
BuildTable = List.Accumulate(ListOfRecords,
                             Table.FromList(ListOfRecords{0}[FileContents][Column1], each {_}),
                             (TableSoFar,NewColumn) => 
                              Table.ExpandTableColumn(Table.NestedJoin(TableSoFar, "Column1", NewColumn[FileContents], "Column1", "Dummy", JoinKind.LeftOuter), "Dummy", {"Column2"}, {NewColumn[ColumnName]})),

// Standard UI
#"Promoted Headers" = Table.PromoteHeaders(BuildTable)

 in

    #"Promoted Headers"