Compare all elements of 2 lists, not necessarily in same order

Question

Q: How to test whether all elements of two lists are the same even though the order may be different?

EXAMPLE: (test-fn '(answered cached unread) '(unread answered cached)) => t

Answer 1

Perhaps you could use your list as a set?

• (cl-set-exclusive-or '(1 2 3) '(3 2 1)) => nil
• (cl-set-exclusive-or '(1 2 3) '(3 2 1 0)) => (0)

You could put it into a function:

(defun order-independent-list-equal (list1 list2)
  "Test if LIST1 and LIST2 hold the same values.
The order of values may be different."
  (not (cl-set-exclusive-or list1 list2)))

• (order-independent-list-equal '(answered cached unread) '(unread answered cached)) => t

There will be a problem if you have multiple instances of the same value though. A more complex version would be something like this:

(defun order-independent-list-equal (list1 list2)
  "Test if LIST1 and LIST2 hold the same values.
The order of values may be different."
  (and (equal (length list1) (length list2))
       (not (cl-set-exclusive-or list1 list2))
       (let ((uniques (remove-duplicates list1)))
         (cl-every
          (lambda (x)
            (equal (cl-count x list1)
                   (cl-count x list2)))
          uniques))))