An integrated transformer that simply filters "candidates" based on whether there is a match in "filter." This could be based solely on matching attributes (definitely the most important component), or could function similarly to the Matcher (allowing for required differences and geometry).
I have attached two workspaces: my "FilterByJoin" transformer, which I use no fewer than 5 times in any workspace I create (and relies, in turn, on two other of my custom transformers), and the beginning conceptual development of a "MatcherFilter" in a few different forms (with some pretty significant performance kinks to work out)
Filtering by matching attributes can currently be achieved in its most-basic form by passing data to a FeatureMerger with candidates as the Supplier and filter as the Requestor, then using the "UsedSupplier" and "UnusedSupplier" outputs, but streamlining that into something that is more transparent in its purpose requires additional steps in a transformer like the "FilterByJoinExample" I've attached!
NOTE: The "Add Attachments" button isn't bringing up any dialogue, so if clicking "Create Idea and Next" posts this and I am not able to add attachments after posting... well, then disregard I guess!
