M Language Transformations

[powerbiexpert22]

Power BI provides most of the transformations like changing type, rename, duplicate , merge etc . in which scenarios or use cases we need M language transformations? 

[Hero1002]

M Language Transformations enable efficient data shaping and manipulation within Power Query.

[v-sgandrathi]

Hi @powerbiexpert22,

Thank you for Connecting with Microsoft Fabric Community Forum.

I wanted to check if you had the opportunity to review the information provided by @danextian , @jaineshp , @MattAllington. Please feel free to contact us if you have any further questions.

Thank you.

[danextian]

Hi @powerbiexpert22 

The UI creates an M code with every applied step so mostly anything* that the UI can't do M becomes very useful. Examles:

• Creating a calendar table
• Flattening a complex JSON file hierarchy
• Splitting start and end date columns into individual rows for each date
• Connecting to mulitple worksheets across different workbooks  -  not just a sheet with a specific name
• Selecting a query to load based on  dynamic or manual conditions
• Transformations that would otherwise require a very complex code if done at the source.

*Mostly anything because although some transformations are theoritically possible, they be computationally expensive and better off done at the source.

[jaineshp · Accepted solution]

Hi @powerbiexpert22 ,

M language becomes essential in these key scenarios:

Complex Conditional Logic:

• Multi-level if-then-else conditions that would take dozens of UI steps
• Dynamic transformations based on business rules

Custom Functions:

• Reusable logic across multiple queries
• When same complex transformation is needed repeatedly

API Integrations:

• Custom web service calls with authentication
• Handling API pagination and JSON parsing

Performance Optimization:

• Combining multiple UI steps into single expressions for better query folding
• Reducing transformation steps for faster refresh

Dynamic Operations:

• Parameterized queries where column names change
• Flexible filtering based on variables

Advanced Text/Date Operations:

• Complex regex patterns or string parsing
• Custom fiscal year or working day calculations

Bottom line: Use M when UI becomes too cumbersome or when you need reusable, dynamic logic.

Best regards,
Jainesh Poojara | Power BI Developer

[MattAllington]

I assume you mean "the UI" provides most transformations, so why do we need to write M code manually. 

Fair question. The short answer is the UI writes the M code for you for most common things, but not everything. The objective is to make the tool usable via the UI, but also make it extensible by having a solid, powerful programming language under the hood. I think MS has done a great job doing this.