THE NEW “LIST OF” SUMMARY OPTION is getting lots of deserved attention:
I’ve found the performance to be excellent and it can now replace the use of Custom Functions, looping scripts etc that were previously used to generate a list of IDs for a found set of records. We’ve also another great use for it – in conjunction with filtered portals it can be used to get the IDs for the currently filtered portal records. This makes it simply to filter a portal, get the list of filtered IDs which can then be used in a multi-key relationship to group those filtered records for further processing.
Check out Andrew Duncan’s post for some unique ways to use this new feature in FileMaker 13, like grabbing a list of id’s from a filtered portal. It’s well worth the read.