unionsWith

unionsWith :: (a -> a -> a) -> [IntMap a] -> IntMap a
containers Data.IntMap.Strict, containers Data.IntMap.Lazy
The union of a list of maps, with a combining operation. > unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])] > == fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]
unionsWith :: Ord k => (a -> a -> a) -> [Map k a] -> Map k a
containers Data.Map.Lazy, containers Data.Map.Strict
The union of a list of maps, with a combining operation: (unionsWith f == foldl (unionWith f) empty). > unionsWith (++) [(fromList [(5, "a"), (3, "b")]), (fromList [(5, "A"), (7, "C")]), (fromList [(5, "A3"), (3, "B3")])] > == fromList [(3, "bB3"), (5, "aAA3"), (7, "C")]