Secondary data source values have to be aggregates which means they can't be dimensions.
Are you able to combine the two files into one excel file?
Hi Aaron - I unfortunately can't combine them into a single file. The actual files are very large workbooks from separate source systems and both are used for numerous other charts. It's good to know I at least didn't miss something very obvious, it felt like there should be a simple way. Thanks!
Have you considered linking the files in Access and then connecting with tableau?
Alternatively you could import them into a free open source database like mysql and query that as your source.
What's the process that gets them into excel? Are you using a relational database with an export process?
How the data gets to the point of consumption is often times how you will be able to fix issues.
Ah, noticed Robert gave a similar suggestion :-)
Thanks both of you for the suggestions. The Excel files are reports output from the source systems (HR systems) and they reside in a SharePoint location. I can only access the data by creating reports in the report builder UI's of the systems. We hope to eventually feed the data to a data warehouse where we'll have much more flexibility and opportunities for automation. I might try linking in Access and see how this goes. We're going to refresh on a weekly basis though, and don't want to create additional manual steps.