Creating Custom Functions in Power Query

In this chapter, we will learn how to create custom Power Query functions in Power BI, covering the planning process, parameters, and the actual creation of the functions. We will start by understanding data requirements and defining the function’s purpose and expected output, then we will learn about the different types of parameters and how to use them to make functions more flexible and reusable, and finally, we will see step by step how to write M code functions, and test and debug them.

Specifically, the following topics will be covered in this chapter:

• Planning for your custom function
• Using parameters
• Creating custom functions

Overall, this chapter will provide a comprehensive guide to creating custom functions in Power BI. From reading this chapter, you can expect to feel more confident in approaching situations where you would need to create a custom function in Power Query. You will have gained hands...

Planning for your custom function

Creating custom functions in Power Query can be a powerful tool for automating and streamlining your data transformation processes. However, before you dive into the world of custom functions, it’s essential to plan your approach carefully. In this section, we’ll explore the key aspects of planning for your custom function, including defining the problem, identifying parameters, and setting clear objectives. Proper planning will ensure that your custom functions are efficient, effective, and aligned with your data preparation needs.

Defining the problem

The first step in planning for a custom function is to clearly define the problem you want to solve. What specific data transformation or manipulation task do you need to perform regularly?

For example, you might need to calculate the rolling average of sales data or create a custom date hierarchy. Identifying the problem is essential as it serves as the foundation for building...

Using parameters

Parameters are a vital component of custom functions in Power Query. They allow you to create dynamic and flexible functions that can be adapted to different datasets and scenarios. In this section, we will introduce parameters, exploring the types of parameters available, how to define them, and best practices for their use.

Types of parameters

Power Query offers several types of parameters that you can use in your custom functions:

• Text parameters: These parameters accept text input, such as column names or descriptions
• Number parameters: Number parameters accept numeric values
• List parameters: You can create lists of values that users can select from
• Table parameters: Table parameters accept tables as input, allowing for more complex data structures
• Function parameters: You can even pass functions as parameters to create dynamic behavior

Defining parameters

To define parameters in Power Query, you need to access the Manage...

Creating custom functions

With proper planning and an understanding of parameters, you’re now ready to dive into creating custom functions in Power Query. This section will guide you through the process of building your custom function, including defining its structure, working with M code, and testing your function.

Defining the function structure

The structure of your custom function is crucial for its functionality and usability. Define the following aspects of your function:

• Name: Choose a descriptive name for your function
• Parameters: Specify the parameters your function will accept and their data types
• Description: Provide a clear and concise description of what your function does
• Result: Determine the expected result or output of your function

Writing M code

Power Query functions are created using the M language, which we touched upon earlier in this book. You’ll need to write M code to define your function’s behavior...

Summary

In this chapter, we explored the process of creating custom functions in Power Query. Effective use of custom functions in Power Query begins with proper planning, forming the cornerstone for building efficient and adaptable functions. This involves defining the problem, identifying parameters, and setting clear objectives to align with your data preparation needs. Parameters, as you learned, play a crucial role in enhancing the flexibility of your functions for various scenarios. The process of creating custom functions encompasses defining the function’s structure, writing M code, thorough testing and debugging, and comprehensive documentation. Armed with these insights, you are well-prepared to leverage the full potential of custom functions in Power Query, with capabilities for seamless data transformation and preparation.

In the next chapter, you will learn more about the techniques and tips on how you can optimize your M code.

Questions

1. What is the first step in planning for a custom function in Power Query?
   1. Writing M code
   2. Testing and debugging
   3. Defining the problem
   4. Creating parameters
2. What role do parameters play in custom functions?
   1. Identifying issues in the code
   2. Enhancing documentation
   3. Making functions flexible and adaptable
   4. Debugging the function
3. Why is it important to provide default values for parameters in custom functions?
   1. To increase the complexity of the function
   2. To make the function less user-friendly
   3. To improve the overall user experience
   4. To avoid testing and debugging
4. What is crucial for defining the structure of a custom function?
   1. Complex M code
   2. Writing extensive documentation
   3. Choosing a descriptive name
   4. Setting default parameter values