discard operation on collections.
Given a collection and a predicate on the collection's elements,
keep returns a new collection containing those elements where the predicate is true, while
discard returns a new collection containing those elements where the predicate is false.
For example, given the collection of numbers:
And the predicate:
Then your keep operation should produce:
While your discard operation should produce:
Note that the union of keep and discard is all the elements.
The functions may be called
discard, or they may need different names in order to not clash with existing functions or concepts in your language.
Keep your hands off that filter/reject/whatchamacallit functionality provided by your standard library! Solve this one yourself using other basic tools instead.