I needed this so I wrote a filter to do it. This filter will return a unique listing of all values in a field. So if you are populating a field with a list of field titles (with a different list in each tiddler) Then this will return the unique listing.
I have the demo here: http://cpashow.tiddlyspot.com/#Unique%20listing%20of%20all%20values%20in%20a%20field I'll add it to the List Management demo soon once I've prettied up the explanation of how its used -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/tiddlywiki. To view this discussion on the web visit https://groups.google.com/d/msgid/tiddlywiki/5380aa34-10b5-4158-aaa4-3ef722d42efa%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.

