I think you can use wild card union with saving three files in same folder.
You can use "path" as unique identifier of each files' category.
Union tables using wildcard search
Use this method to set up search criteria to automatically include tables in your union. Use the wildcard character, which is an asterisk (*), to match a sequence or pattern of characters in the Excel workbook and worksheet names, Google Sheets workbook and worksheet names, text file names, JSON file names, .pdf file names, and database table names.
When working with Excel, text file data, JSON file, .pdf file data, you can also use this method to union files across folders, and worksheets across workbooks. Search is scoped to the selected connection. The connection and the tables available in a connection are shown on the left pane of the Data source page.
To union tables using wildcard search
- On the data source page, double-click New Union to set up the union.
- Click Wildcard (automatic) in the Union dialog box.
- Enter the search criteria that you want Tableau to use to find tables to include in the union.For example, you can enter *2016 in the Include text box to union tables in Excel worksheets that end with "2016" in their names. Search criteria like this will result in the union of May2016, June2016, and July2016 tables (Excel worksheets), from the selected connection. In this case, the connection is called Sales, and the connection made to the Excel workbook containing the worksheets you wanted was in the quarter_3 folder in the sales directory (e.g., Z:\sales\quarter_3).
- Click Apply or OK to union.