Dr. Racket: Deleting Items from a List Using Abstract List Functions

advertisements

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))

Thanks!

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)

Related Articles

Deleting items from a list box after you set DataSource

I have a small requirement and that is as follows: I am populating a ListBox using stored procedures and the ListBox is populated as follows: lstItems.DisplayMember = "emp_name" lstItems.ValueMember = "login_id" lstItems.DataSource = a

jquery delete items from the list after one click

can you help me with an ideea how i could remove items from a list after i click an item? let's say i have a list with 5 items and i press on the 3rd item, i want item4 and item5 to be removed. I want to remove all items after the one clicked in the

Deletes items from a list, using another list as indices

I have a list primeList and another list ls. primeList is a list full of integers, and I need to delete the values from ls which have an index that is in primeList. For example if primelist = [1, 3 , 5] and ls = [1, 2, 3, 4, 5, 6, 7], then indexes 1,

Deleting items from the list using LINQ

This question already has an answer here: Using LINQ to remove elements from a List<T> 14 answers I have a List of type some entity List public class OrderLine { public string productCode; public int quantity; } i need to remove items from the above

How to delete items from the list in Fragments?

I want to delete the items from the fragments. When long click on the items than a action bar is changed and a delete button appears. I click on the delete button The item seems to be deleted from the list view. But when I restart the app the item ap

Delete items from the list in React js

I am creating a To-do app & I am not able to write the code for deleting the elements of the list when we click them. I want the specific item to delete when a user clicks on it class Todo extends React.Component { constructor(props) { super(props);

Deleting items from a list in a list

I have the data below, which is a list of lists. I would like to remove the last two elements from each list, leaving only the first three elements. I have tried list.append(), list.pop() but can't seem to get them to work. I guess it is not possible

Delete items from the list if they are within a given range

I want to remove every item from a sorted list, when it is within 100 seconds from one of the previous events. Example: event_list = [3, 10, 12, 140, 140, 150, 300] filtered_event_list = [3, 140, 300] I have the following piece of code that seems to

Delete items from a list

I have the following list n = 1:10 s = c("aa", "bb", "cc", "dd", "ee") b = c(TRUE, FALSE, TRUE, FALSE, FALSE) x = list(n, s, b, 3) For a vector v we can remove elements like this: v[-(1:2)]. But how do we

Deleting Items from the List Containing Null Using Iterator

List<Integer> list = new ArrayList<>(); list.add(12); list.add(null); list.add(22); list.add(32); System.out.println(list); Iterator<Integer> iterator = list.iterator(); while(iterator.hasNext()){ Integer a = iterator.next(); System.out.