Advanced Power Query: M Language Masterclass

(Go beyond the point-and-click User Interface in Power Query and learn to solve advanced data cleaning problems using the M language...)

Masterclass Overview

This Masterclass is for Data Analysts who already use the Power Query’s UI and constantly come across more complex problems that the UI can’t solve.
After the Masterclass participants will be able to write dynamic queries that survive source changes, turn repetitive cleaning into reusable functions, debug any M script including AI-generated code, and know when to write M vs. reach for AI.

Masterclass Content

1. How M actually works

• let…in, steps, and how a query evaluates
• Lists, records, and tables
• Reading the M behind UI steps so you can edit it confidently

2. Lists, Records, and Tables in depth

• Constructing and transforming each type
• Converting between them (the operations that unlock most advanced work)
• Patterns: unpivot/pivot and split/combine columns programmatically

3. Iteration and looping without a loop

• Understanding each _
• Solving advanced looping problems with List.Generate and List.Accumulate

4. Custom functions that scale

• Writing, parameterizing, and documenting your own functions
• Building a small reusable function library

5. Error handling and resilient queries

• try…otherwise and reading error records
• Queries that degrade gracefully instead of failing the whole refresh
• Defending against renamed columns, missing files, and bad rows

6. Common Recipes for tricky cleaning problems

• messy/merged headers,
• complex data combining patterns

7. AI-assisted M development

• Using Copilot / Claude / ChatGPT to draft, explain, and refactor M
• Prompts that produce good M: name exact columns, give sample rows, show expected output, iterate

The masterclass ends with a competitive challenge where participants solve a comprehensive problem for a prize.

Prerequisites and Technical Requirements.

• Excel - Microsoft 365 and/or Power BI Desktop installed
• Comfortable with the Power Query UI (Get Data, transforms, merge/append); no prior M coding needed, but able to follow along in the formula bar / Advanced Editor
• An AI assistant (Copilot, Claude, or ChatGPT) for Module 7