Why I’m Excited About The New DAX EvaluateAndLog() Function

If you aren’t active on Twitter or LinkedIn (or you don’t spend a lot of time on them) you may not have heard about the new EvaluateAndLog() function. It’s not documented yet and not mentioned on any of the official blogs, but you can read about it in the last two posts on Jeffrey Wang’s blog here:

[If you’re wondering who Jeffrey is, he’s one of the resident geniuses that Microsoft employs on the Power BI development team – he’s one of the people Marco and Alberto go to when they need help ]

I think this is the most exciting thing to happen in DAX since the introduction of variables. Why? Well we all know that writing DAX can be hard, and part of why it’s hard is that it’s hard to debug. Things like Tabular Editor 3’s DAX Debugger can be really useful but the EvaluateAndLog() function is the first time the AS/Vertipaq engine has given us the ability to see the intermediate values used by a DAX expression to calculate its output without lots of tedious commenting and uncommenting or the use of ConcatenateX(). Have you ever wanted a watch window to see what’s going on inside a measure? Have you ever wanted to debug your DAX by printing out values to a console or a log file? Well that’s what EvaluateAndLog() allows you to do.

It’s still early days: Jeffrey hasn’t blogged about all of its secrets yet and the functionality needs a bit of polishing. That said, if you’re passionate about DAX I strongly suggest you check it out right now because it will make your life a lot easier.