I'm not sure if this will work but could you try making a set that excludes the Nulls for the filter?
Please find my approach
- Right-click a dimension and select Duplicate.
- Drag the original field to the Filters shelf and include all values.
- Right-click the dimension on the Filters shelf and select Show Filter.
- Open the drop-down menu in the upper right corner of the filter card and then select Only Relevant Values.
- Place the duplicate field on the Filters shelf, select all values except the null values, and then click OK.
Dual axis test.twbx 10.3 MB
Thank you to both of you for your ideas (and for everyone else who helped out) - sorry for the slow reply - I've been trying to work out a solution for this one!
Sadly excluding the NULLS removed the secondary dataset, so I needed a way to keep them in, but not have the NULL in the filter.
The solution involved going outside of Tableau and using Mapbox - I created a polygon map in Mapbox (with the deprivation data) which I then used as a background map within Tableau. Having only one dataset running in Tableau meant I removed the NULL issue.
It has some downsides - the deprivation data values can't be 'accessed" but it's role was always to give a guide so it works in this instance.
Thanks again for all the help and ideas.