In this Power Query masterclass, we solve a real-life advanced data cleaning problem using Power Query and M language. The data is messy, with merged headers, multiple header rows, totals in between, data split into different sections, changing stage columns, and multiple Excel files coming from a folder. Instead of cleaning everything manually, we build a dynamic Power Query solution that can handle this structure automatically.
Along the way, we use M language concepts like Folder.Files, Excel.Workbook, Table.TransformColumns, List.PositionOf, Table.Range, custom functions, unpivoting, grouping, and dynamic column handling. The goal is not just to show the final answer, but to explain the thinking framework behind solving advanced data cleaning problems in Power Query. Once you understand the pattern, you can apply the same approach to your own messy Excel files, reports, exports, and business data.
