So when given two lists, how do I remove elements in one list from another using only map, filter or foldr? I can't use explicit recursion or lambda either.
The lists consist of only numbers that are sorted in ascending order.
For example, if given (list 1 2 3) and (list 1 3 5), I want to remove all of the second list's elements from the first list. The output I want is (list 2). If given (list 4 5 6) and (list 2 3 5), I would get (list 4 6).
I'm guessing the final code would be something like:
(define (fn-name list-one list-two) (filter ... list-one))
Given that you're using Racket, we can write a simple solution in terms of some of the built-in abstract list functions and without using explicit
lambdas, we only need a little help from
SRFI-26. Try this:
(require srfi/26) (define (difference lst1 lst2) (filter-not (cut member <> lst2) lst1))
It works as expected:
(difference (list 1 2 3) (list 1 3 5)) => '(2) (difference (list 4 5 6) (list 2 3 5)) => '(4 6)