#sets
Union, intersection and difference.
- difference_by(a, b, key)Keep the items of one list whose key doesn't appear in another, preserving order.
- intersection_by(a, b, key)Keep the items of one list whose key also appears in another, preserving order.
- union_by(a, b, key)Merge two lists, keeping the first item for each key, in a predictable order.