Has anyone seen a custom function that will pick-out all items in a list that have a particular pattern.

In my case I would like all the items that start with the word 'letter'

You are definitely challenging what a good key integrity is characterised with, and ought to reconsider the realm you're in with filemaker.

However does this something in that direction:

http://www.briandunning.com/cf/771

--sd

This can be done by calculation - no custom function required:

FilterValues ( 

listOfValues ; 

Substitute ( ¶ & listOfValues ; [ ¶ & prefix ; "§" ] ; [ ¶ ; "¶±" ] ; [ "§" ; ¶ & prefix ] ) 

)

Note that this is case-sensitive - though it could be adjusted, if required.