As I’m sure you’ve guessed by now I’m a big fan of dynamic M parameters in Power BI. They’re easy to use in Power BI Desktop but what if you want to use them in your own DAX queries? Documentation for this is coming soon, but in the meantime I thought it would be useful to show the additions to DAX query syntax to support them – something you can see for yourself if you take a look at the DAX queries generated by Power BI Desktop using Performance Analyzer.
Last week’s post showed an M function that took Power Query diagnostics data and formatted in a way that made it suitable for visualisation in a Power BI Decomposition Tree visual. This is great for understanding what’s going on at a high level, but by doing this you also lose a lot of detailed information from the diagnostics logs that could be useful for performance tuning.
DMVs (Dynamic Management Views) are, as the Analysis Services documentation states, “queries that return information about model objects, server operations, and server health”. They’re also available in Azure Analysis Service, Power BI and Power Pivot and are useful for a variety of reasons, for example for generating documentation.
One of the most common issues faced when calling web services in M is that the the easiest way of doing so – creating a function that calls the web service, then calling the function once per row in a table using the Invoke Custom Function button – is very inefficient. It’s a much better idea to batch up calls to a web service, if the web service supports this, but doing this forces you to write more complex M code.
This is a very short post! A lot of people have blogged about how to convert numbers between different bases in M (see for example Maxim Zelensky’s very elegant solution for converting from binary to decimal), but today I noticed there was a very easy way to convert a decimal number to hexadecimal using the Number.ToText() function: you just need to use “x” in the second parameter.
I was looking at the list of M functions supported in custom connectors and not in Power BI Desktop (using the technique I blogged about here) in the latest version of the Power Query SDK when I came across an intriguing new function: List.ParallelInvoke(). It doesn’t seem to be documented anywhere, but I think I’ve worked out what it does and it’s very exciting!
CSV files are one of the most commonly used data sources in Power BI and Power Query/Get&Transform, and yet the documentation for the Csv.Document M function is very limited and in some cases incorrect. In this rather long post I’ll show you as many of the capabilities of this useful function as I’ve been able to discover.