Tableau is a Swiss army knife for data visualization, with a bunch of component tools – the view types, calculated fields, table calculations, custom SQL, mapping, performance optimization, etc. As I’ve been learning Tableau I’ve been mastering new bits. Lately I’ve been exploring Tableau’s Show Missing Values feature, otherwise known as “date padding” or sometimes “domain padding”, and made an interesting discovery.
Here’s a not uncommon problem with blending on the Tableau forums: there’s data in the primary data source, and linking fields in the secondary, but some values in the secondary that don’t exist in the primary. For example, there might be extra dates recorded in the secondary data. Historically, the only ways I’ve known around this have been to pad out the primary by reworking the data source or using Custom SQL in Tableau. I got curious as to whether Show Missing Values would pad the data sufficiently to do a blend, and yes, it does:
At first glance, this is extremely cool, and takes Tableau version 8’s new feature of not even needing the linking field to a new level – with date padding, you don’t even need linking values to blend!
What happened here (among other things) is that Show Me turned Show Missing Values off. We can turn Show Missing Values back on, but in this case that doesn’t bring the padding back unless we add a table calculation to the view that has the Compute Using on Date. There is a logic here to how Tableau works that I don’t completely understand yet, I’m filling up workbooks with test cases, asking questions of and trading ideas with Joe Mako (who gave me some awesome feedback on this post), and looking forward to sharing what I find and learning from others. If you’re diving into domain padding yourself, let’s talk!