Seems to work for me on a local workbook. Could you attach an example?
That data I have is stored on Tableau Server.
I noticed that your reply mentioned a local workbook, so I extracted the data into a local datasource and it worked fine.
As soon as I change to reading from the server, it goes back to being #Error
I am thinking this might be a function of however we are publishing the String to Tableau Server, which is sorted when Tableau Desktop Extracts.
can you try with Regular Expression instead of using Trim and left function. Something like below.
if not isnull([String]) then