unionsWith package:multi-containers

Union a number of tables with a combining function for duplicate keys.

unionsWith (++) [fromList [(1,'a',"b"),(1,'b',"c"),(2,'a',"b")], fromList [(1,'a',"c"),(2,'b',"d"),(3,'c',"e")]]
=== fromList [(1,'a',"bc"),(1,'b',"c"),(2,'a',"b"),(2,'b',"d"),(3,'c',"e")]

Union a number of tables with a combining function for duplicate keys.

let f r c a a' = show r ++ ":" ++ show c ++ ":" ++ a ++ "|" ++ a' in do
unionsWithKeys f [fromList [(1,'a',"b"),(1,'b',"c"),(2,'a',"b")], fromList [(1,'a',"c"),(2,'b',"d"),(3,'c',"e")]]
=== fromList [(1,'a',"1:'a':b|c"),(1,'b',"c"),(2,'a',"b"),(2,'b',"d"),(3,'c',"e")]