I often get asked if there is an easy way to create documentation for DAX measures when using Power Pivot for Excel. I am not a big fan of documentation for the sake of it, but I do see value in having “some” appropriate level of documentation. I think a good balance of the right amount of documentation vs the effort to write and maintain the documentation is to use the Power Pivot UI itself. I explain how I do it below.
Writing DAX Measures From Within Excel
I always teach students at my Power BI training courses to write their measures from within Excel via the “new measures” dialog box (and specifically not to write them from within the Power Pivot window). The process is always as shown below.
- Set up a pivot table that has some relevance to the measure you are writing, then click in the pivot table (shown as 1 below)
- Select Power Pivot Menu \ Measures* \ New Measure* as shown below (*called Calculated Field in Excel 2013)
The reasons I teach students to do it this way are simple.
- You get a dialog box/wizard that shows you every step that is required to complete the task. Just complete each step one at a time and you can’t go wrong.
- You get to check the measure for errors before completing it (shown as 2 below).
- Once you add the measure to your pivot table (shown as 3), you get to see immediately if it is working as you expected.
And there is a fourth reason to use the wizard that is less obvious. The Description box (shown as 4 above) is a great place where you can make notes about your DAX formulas (aka documentation). In Power BI Desktop you can add comments into your DAX expressions, but this is not possible in Excel, so the description box is the best option you have.
Create Your Documentation
If you diligently add comments into the Description box above, you will then be able to extract this information into a documentation page using the Power Pivot Utilities Toolbar. I have previously reviewed this great little tool here, so you can go back and read about it if you missed it.
- First you should download and install Power Pivot Utilities here. (Excel 2013+ only).
- You should then also download and install DAX Studio here (also needed for the documentation step)
After installing both tools, you will then see the PP Utilities Toolbar in Excel (shown as 1 below)
Click on List Measures (shown as 2 above). After a few seconds, you will see a new page in your Workbook called “Measures” like shown below. Note the “Description” column on the right hand side. This column is sourced directly from the information entered into the Description box shown further up the page.
What’s more, if you select the measures on your page (Shown as 1 below) and then click Format DAX Expressions (2 below), the measures will be nicely formatted so they are easy to read.
This page is then your documentation and you can refer to it at any time you need to see the big picture.
Always Up to Date
One important feature of this type of documentation is that it is very easy to maintain. If you make changes to any of the measures or comments in your data model, you can simply re-run the extract process so you have an up-to-date list of all the measures. You can also do the same for Calculated Columns and also relationships.
What About Excel 2010?
Unfortunately the Power Pivot Utilities Addin only works for Excel 2013+ But all is not lost. It is possible to extract the Measures from your Data Model manually using DAX Studio. You can read my blog post about how to do that (and other cool things) with DAX Studio here