Understanding M Language – The Backbone of Power Query

Power Query is an essential tool for data transformation in Excel and Power BI, and at its core lies M Language. This powerful, functional programming language allows users to perform advanced transformations, automate workflows, and create custom queries.

In this guide, we’ll explore M Language basics, its syntax, and how you can leverage it to enhance Power Query operations.

1. What is M Language?

M Language is the scripting language used in Power Query for data transformation and manipulation. It enables users to: ✅ Automate complex data cleansing and transformation tasks.
✅ Perform operations that are not possible through the Power Query UI alone.
✅ Optimize queries for better performance and scalability.

Unlike DAX, which is used for calculations and measures in Power BI, M Language is designed for data extraction and transformation.

2. Understanding M Language Syntax

M is a case-sensitive language and follows a functional approach. Let’s break down its key components:

A. Basic Structure of an M Query

let
    Source = Excel.CurrentWorkbook(){[Name="SalesData"]}[Content],
    FilteredRows = Table.SelectRows(Source, each [Sales] > 5000),
    SortedData = Table.Sort(FilteredRows,{{"Sales", Order.Descending}})
in
    SortedData

Explanation:

let – Defines variables and transformation steps.
Source – Loads data from an Excel table named “SalesData”.
FilteredRows – Filters records where Sales > 5000.
SortedData – Sorts the filtered results by Sales in descending order.
in – Returns the final output.

B. Key Functions in M Language

Function	Description
`Text.Combine()`	Joins multiple text values into a single string.
`Date.AddDays()`	Adds days to a given date field.
`Table.SelectRows()`	Filters rows in a table.
`Table.Sort()`	Sorts data based on a specific column.
`Record.FieldValues()`	Extracts values from a record.

3. Working with M Language in Power Query

A. Editing M Code in Power Query

Open Power Query Editor in Excel or Power BI.
Click on Advanced Editor.
Modify or write your M query.
Click Done to apply the changes.

B. Creating Custom Columns with M Language

You can create a new column using M functions:

Table.AddColumn(Source, "DiscountedPrice", each [Price] * 0.9)

This applies a 10% discount to the Price column.

4. Best Practices for Writing M Code

📌 Use meaningful variable names to improve code readability.
📌 Filter data as early as possible to enhance performance.
📌 Modularize queries by breaking them into smaller steps.
📌 Document your code using comments (// This is a comment).

Conclusion

✅ M Language is the backbone of Power Query, enabling advanced data transformation and automation.
✅ It follows a functional programming approach, making it flexible and powerful.
✅ Mastering M Language helps in optimizing queries and unlocking full Power Query potential.