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Category: DAX

Power BI Field Parameters and None Options

Barney Lawrence votes None of the Above:


Field Parameters
 are one of my favourite recent additions to Power BI. The ability to turn a single chart into potentially dozens changes the way we think about putting variations of visuals on the page. It was a real wow moment for a client recently when I showed how field parameters for 5 fields and 5 measures could produce a single report page that replaced 25 of their existing reports.

While they theoretically don’t allow you to do much that you couldn’t previously with a disconnected slicer and a lot of DAX they build it faster and without the need to get heavily in to coding DAX. Anything that lowers the difficulty bar for users trying to make the most out of Power BI is a good thing in my book.

There are a couple of issues Barney has with them as they stand now but there are workarounds.

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Variables in DAX

Marco Russo and Alberto Ferrari show us how to use variables in DAX:

Variables were introduced in DAX in 2015 and so far, they have proven to be the best enhancement of the DAX language ever. When presented with the concept of variables, most newbies focus on performance improvement, thinking that you introduce variables in your code mainly to obtain better performance. Although variables can improve performance, performance is a minor advantage. There are several more important considerations that should encourage any DAX developer to make extensive use of variables. In this article we share a few considerations, along with best practices about variables and DAX.

Read on to see what makes variables so powerful.

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Report-Level Measures in Power BI

Soheil Bakhshi explains the concept of report-level measures:

Report level measures are the measures created by the report writers within a Thin Report. Hence, the report level measures are available within the hosting Thin Report only which means the report level measures are not written back to the underlying dataset and hence they are not available to any other reports.

Read on to see how you can create one. I don’t think I’d ever heard them called that before but the name makes sense.

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Making DAX’s SWITCH Run Fastest

Marco Russo and Alberto Ferrari explain when SWITCH is fast and when it’s not so fast:

The SWITCH function in DAX is widely used to define different execution paths depending on the condition of an expression. A very common case is when we want to check the state of a slicer, so that the selection made by the report user directly affects the result of a DAX formula.

Read on for three separate cases and how they can affect the performance of the SWITCH function.

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KEEPFILTERS in DAX

Marco Russo and Alberto Ferrari explain how the KEEPFILTERS function works:

KEEPFILTERS is a CALCULATE modifier used to change the way CALCULATE merges new filters with the outer filter context. Indeed, the default behavior of CALCULATE is to override existing filters. By using KEEPFILTERS you ask CALCULATE to add the new filter to the outer filter context, instead of overriding the outer filter.

Read on for the explanation and a demo.

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Applying Forecasts with Known Seasonal Behavior in Power BI

Imke Feldmann begins a series on seasonality in Power BI:

Please note, that the monthly variation I am using in this example is taken from an existing table and not derived by statistical methods like the Excel FORECAST.ETS.SEASONALITY function. Here, we simply apply an existing distribution to expected future sales, but I will cover forecasts using those statistical methods in upcoming blogposts.

Todays starting point is a request to calculate how many sales to expect until the end of the year and then distribute the expected sales according to a list of monthly %, which are all different, because there is an expected seasonality in the sales:

Click through to see how this all works.

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Counting Employees by Period with DAX

Matt Allington solves a common problem:

I’m calling this article, “How many employees by period”. Staff come and go for different reasons. In some companies, the number of staff can change over time. The principles used in this article can also be used in other instances.  There can be staff moving in and out of departments, on and off of projects, etc. The technique can also be used to work out how many staff were on leave, how many off sick, how many tickets were open in a support queue, or any other concept that has a start and end date in a transactional table.

Read on for Matt’s answer but be sure to check out the comments as there are some other good solutions in there.

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Context Transition in DAX

Marco Russo and Alberto Ferrari explain the idea of context transition in DAX:

Let us state this from the very beginning: context transition is a simple concept. It is a powerful feature aiming to simplify the authoring of DAX code. That said, most new DAX developers find context transition hard to understand, and they consider it to be the major reason behind incorrect results. There are two reasons for developers to feel this way:

– A solid understanding of the difference between the row context and the filter context is an important prerequisite to understand and master the concept of context transition.

– You need to remember when and how the context transition works. Most errors involving context transition are due to the developer forgetting to take the context transition into account, rather than not knowing how it works. Once they realize that context transition is happening, the code suddenly makes sense.

Read on to understand more about the idea of context transition.

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