The video defines DAX User Defined Functions as reusable, parameterized snippets of DAX that behave like functions in traditional programming languages. Hopkins demonstrates the new syntax and shows that functions are declared using the FUNCTION keyword with typed parameters and a clear return expression. In his examples, functions accept scalar and table inputs and can return a specific data type, which helps with predictability and authoring confidence. Hopkins positions the change as one of the most significant shifts to DAX authoring in years because it brings familiar programming patterns into the tabular model. He notes that DAX UDFs let authors create named, parameterized functions that can be reused across measures, columns, and visuals. Importantly, the video emphasizes that the feature must be enabled manually in desktop preview settings before it can be used.
Definition of UDFx in DAX Query
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- Finally, he underscores the importance of team governance so naming conventions, parameter types, and reuse policies remain consistent as function libraries grow.
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- In the previous EXPR example, the argument of BestCustomers was a measure reference, Sales Amount.
- The difference is very important to understand because using the wrong parameter-passing mode is likely to generate glitches in your code that are hard to debug.
With UDFs, you can create a https://p1nup.in/ centralized calculation that can return the Running Total for any measure. In the expression for each of the variables, we’ll check the hierarchy using the ISINSCOPE DAX function and then use SWITCH to decide upon the calculation. Evaluates an expression in a context modified by filters. The function produces the correct result; once executed, the result contains 1,807 customers, some of which are shown in the following screenshot.
There are a couple of ways to calculate Running Totals in Power BI, and one such method is using the Maximum Date logic. I have used a parameter _field that takes any measure as an input. Next, I dragged that measure onto my matrix visual, and you can see below how easily the conversion and symbols were applied across all geographies. You can’t just simply create UDFs like you’ve been creating measures till now.
To use your other apps again, you can unpin the screen. If you want to see built-ins and your UDFx together with some tidy filtering, you cannot do it in one go. This is a more visual way to see how the function evaluates with expr vs val. Let’s take a closer look at the parameterMode options val and expr. Used properly, they behave quite differently and can produce different results. You can use UDFx in a visual calculation, just not this exact one.
Once done with defining the function CurrencyConv, I created a measure called Dynamic Profit and called the CurrencyConv by passing the Total Profit measure. Imagine having a data model that holds data for various geographies, and you’ve created several visuals showing geography-wise data. In the Model view, I selected each measure and, using the Dynamic format string option, called the FormatString() created in the previous step.
How UDFs Work
In a recent YouTube video, Wyn Hopkins MVP explains the new DAX User Defined Functions that arrived with the September 2025 update to Power BI. The author walks viewers through what the feature does, why it matters, and how authors can begin experimenting while the feature remains in preview. Overall, the video provides a practical tour intended for modelers and analysts who write DAX regularly. In this final step, I’ve created Till Date Sales measure that calls the CumulativeDates function, and I’ve passed the Total Sales measure as the parameter. Once all the 3 variables are created, SWITCH is used again in the RETURN section to pass the correct variable calculation based on the _measure value. With this use case, I have created a function that returns the previous value for any Date hierarchy level and for any measure that’s passed into the function.
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- This may seem like a small detail, but it is the difference between a function written by a newbie and a function written by a DAX professional.
- Let’s take a closer look at the parameterMode options val and expr.
Anatomy of a DAX function
You use SELECTEDMEASURE() and call your UDFx like any other function. Marco Russo is a business intelligence consultant and mentor. Marco founded SQLBI with Alberto Ferrari, and OKVIZ is a spinoff of the company dedicated to Power BI Custom Visuals. As you can see below, Cumulative totals (MTD, QTD, and YTD) are calculated quite easily across all the date hierarchies. I’d recommend using the DAX Query view because its DAX-friendly design makes it more relatable.
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To be able to create and use UDFs, you can use either the DAX Query view or the TMDL view in Power BI Desktop. Developers can also specify the type of parameters, choosing among a broad range of options, listed in the following table. To avoid confusion, we always use Pascal case for user-defined functions.
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In the function defined above, both a and b are value parameters. By default, arguments of functions are value parameters. However, it is possible to use EXPR to force them to be treated as expressions. The difference is very important to understand because using the wrong parameter-passing mode is likely to generate glitches in your code that are hard to debug. By default, when you create a responsive search ad, headlines and descriptions can appear in any order. You can control where individual headlines and descriptions appear in your ad by pinning headlines and descriptions to specific positions.
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UDFx behave like regular built-in functions such as CALCULATE or SUM. They can accept zero or many parameters with specific types and subtypes. The output depends on what your UDFx does and which functions or expressions it uses, though you can cast or convert the result if needed. In short, handle UDFx outputs the same way you would handle outputs from built-in functions.
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Learn how to Pin headlines and descriptions to specific positions. Google will optimize the placement of all other assets while ensuring they remain relevant to the user’s search query. The video argues that UDFs improve maintainability because a single, centralized function can replace repeated long expressions dispersed across measures. As a result, teams can enforce consistent business rules and reduce the risk of subtle calculation differences between visuals.
When defining parameters, we have the option to choose the parameter type, subtype, and parameter-passing mode. The most crucial detail is the parameter-passing mode; we dedicate a specific section to this topic later on in the chapter. There are two parameter-passing modes, and the choice of parameter-passing mode significantly impacts the function’s behavior. In contrast, the parameter type and subtype are less relevant. Move between steps in the navigation menu to easily review and resolve potential issues with your targeting, bidding, budget, or other campaign settings. If you want to list all your UDFx, you can use a DAX query.