union package:mono-traversable

Get the union of two containers.
Combine two maps. When a key exists in both maps, apply a function to both of the values and use the result of that as the value of the key in the resulting map.
Combine a collection of SetContainers, with left-most values overriding when there are matching keys.
Combine a list of maps. When a key exists in two different maps, apply a function to both of the values and use the result of that as the value of the key in the resulting map.