Hi Jesse - have you tried creating an aggregate that has the min and max for what you want and then joining that back to the data?
Help me understand the end goal - Tableau Prep is a tool to clean and reshape data the is then submitted to Tableau for analysis -
- in tableau prep you are creating a higher level of if data n the the data file - similar to what you would do with an LOD expression in Tableau -
The actual analysis is done in Tableau
I actually use Prep for a lot more than just Tableau workbooks/dashboards