Topic: [challenge] A03 : Find the number of elements of a list without using LENGTH

[ronjonp]

John, please clarify what is expected on an empty list.
I guess, if '(1 2 3 4 5 6 7) -> 6, then '(1) -> 0 and '() - > nil

The 'native' length function does not work this way.
(length  '(1 2 3 4 5 6 7)) -> 7
(length  '(1)) - > 1
(length  '()) -> 0

Late to the party but I'd say it should return 0 rather than nil if you're mimicking the length function.

Code - Auto/Visual Lisp: [Select]

1. (length nil)
2. 0

[Stefan]

John, please clarify what is expected on an empty list.
I guess, if '(1 2 3 4 5 6 7) -> 6, then '(1) -> 0 and '() - > nil

The 'native' length function does not work this way.
(length  '(1 2 3 4 5 6 7)) -> 7
(length  '(1)) - > 1
(length  '()) -> 0

I agree. See Edit note in my first post. John decided to have it that way.

Acknowledged but if you are using/building this function in a larger procedure you may want to control flow via an conditional like IF or COND ?easier?.
(if (my-count-list aList) ...

Well, I play for the fun, but I don't see where this function might be used
(if (my-count-list aList) ... is similar to (if aList.

[JohnK]

I agree Stefan but this will come up again in later challenges--some of which are actually more useful functions-. I need to determine how many and we can just make this one return nil and let the later challenges error out or return what the programmer wants.

[Stefan]

Don't worry John, it is really fun and I appreciate your initiative.

Here is another

Code - Auto/Visual Lisp: [Select]

1. (defun my-count-list-stef3 (l)
2.   (cond
3.     ((cdr l) (1+ (my-count-list-stef3 (cdr l))))
4.     (l 0)
5.   )
6. )

[JohnK]

No problem. I have a file with about 18/19 challenges typed up so far and I keep ACCORECONSOLE running on the side so I can test out any solution I type up. Works good but it's a lot of work.

[apricot125]

Code: [Select]

(defun _length (lst)
  (cond ((not (cdr lst)) 0)
        (t (1+ (_length (cdr lst))))
  )
)

[dexus]

Here is a different solution:

Code - Auto/Visual Lisp: [Select]

1. (defun length-dexus (lst / ret)
2.   (if (vl-consp lst)
3.     (apply '+ (cdr (mapcar '(lambda (x) 1) lst)))
4.   )
5. )

Unless if vl-consp is not allowed, it would be something like this:

Code - Auto/Visual Lisp: [Select]

1. (defun length-dexus (lst / ret)
2.   (setq ret (apply '+ (mapcar '(lambda (x) 1) lst)))
3.   (if (/= ret 0) (1- ret))
4. )

[JohnK]

Code: [Select]

(defun _length (lst)
  (cond ((not (cdr lst)) 0)
        (t (1+ (_length (cdr lst))))
  )
)

I like that, apricot125.

[JohnK]

Here is a different solution:

Code - Auto/Visual Lisp: [Select]

1. (defun length-dexus (lst / ret)
2.   (if (vl-consp lst)
3.     (apply '+ (cdr (mapcar '(lambda (x) 1) lst)))
4.   )
5. )

Unless if vl-consp is not allowed, it would be something like this:

Code - Auto/Visual Lisp: [Select]

1. (defun length-dexus (lst / ret)
2.   (setq ret (apply '+ (mapcar '(lambda (x) 1) lst)))
3.   (if (/= ret 0) (1- ret))
4. )

Correct. VL-CONSP--or anything that starts with VL--is not allowed and would be disqualified.

[dexus]

[...]

Correct. VL-CONSP--or anything that starts with VL--is not allowed and would be disqualified.

I see, well, all vl-consp does is check if the type is a list, so this should do exactly the same thing:

Code - Auto/Visual Lisp: [Select]

1. (defun length-dexus (lst / ret)
2.   (if (eq (type lst) 'LIST)
3.     (apply '+ (cdr (mapcar '(lambda (x) 1) lst)))
4.   )
5. )

[Stefan]

Here is a different solution:

Code - Auto/Visual Lisp: [Select]

1. (defun length-dexus (lst / ret)
2.   (if (vl-consp lst)
3.     (apply '+ (cdr (mapcar '(lambda (x) 1) lst)))
4.   )
5. )

Not quite different...

[dexus]

Here is a different solution:

Code - Auto/Visual Lisp: [Select]

1. (defun length-dexus (lst / ret)
2.   (if (vl-consp lst)
3.     (apply '+ (cdr (mapcar '(lambda (x) 1) lst)))
4.   )
5. )

Not quite different...

Whoops, I didn't see that one, sorry about that.

[Marc'Antonio Alessi]

>>> EDIT for null list (IMHO I prefer results LENGHT like…)

Code: [Select]

(defun ALE_Length (l / p c)
  (and
    l
    (setq c 0)
    (while l
      (cond
        ( (setq p (cddddr (cddddr (cddddr l)))) (setq l p  c (+ c 12)) )
        ( (setq p (cddddr (cddddr (cdddr  l)))) (setq l p  c (+ c 11)) )
        ( (setq p (cddddr (cddddr (cddr   l)))) (setq l p  c (+ c 10)) )
        ( (setq p (cddddr (cddddr (cdr    l)))) (setq l p  c (+ c  9)) )
        ( (setq p (cddddr (cddddr         l)))  (setq l p  c (+ c  8)) )
        ( (setq p (cddddr (cdddr          l)))  (setq l p  c (+ c  7)) )
        ( (setq p (cddddr (cddr           l)))  (setq l p  c (+ c  6)) )
        ( (setq p (cddddr (cdr            l)))  (setq l p  c (+ c  5)) )
        ( (setq p (cddddr                 l))   (setq l p  c (+ c  4)) )
        ( (setq p (cdddr                  l))   (setq l p  c (+ c  3)) )
        ( (setq p (cddr                   l))   (setq l p  c (+ c  2)) )
        ( (setq p (cdr                    l))   (setq l p  c (+ c  1)) )
        ( (setq l nil) )
      )
    )
  )
  c
)

Code: [Select]

Old version:
(defun ALE_LengthO (l / p c)
  (setq c 0)
  (while l
    (cond
      ( (setq p (cddddr (cddddr (cddddr l)))) (setq l p  c (+ c 12)) )
      ( (setq p (cddddr (cddddr (cdddr  l)))) (setq l p  c (+ c 11)) )
      ( (setq p (cddddr (cddddr (cddr   l)))) (setq l p  c (+ c 10)) )
      ( (setq p (cddddr (cddddr (cdr    l)))) (setq l p  c (+ c  9)) )
      ( (setq p (cddddr (cddddr         l)))  (setq l p  c (+ c  8)) )
      ( (setq p (cddddr (cdddr          l)))  (setq l p  c (+ c  7)) )
      ( (setq p (cddddr (cddr           l)))  (setq l p  c (+ c  6)) )
      ( (setq p (cddddr (cdr            l)))  (setq l p  c (+ c  5)) )
      ( (setq p (cddddr                 l))   (setq l p  c (+ c  4)) )
      ( (setq p (cdddr                  l))   (setq l p  c (+ c  3)) )
      ( (setq p (cddr                   l))   (setq l p  c (+ c  2)) )
      ( (setq p (cdr                    l))   (setq l p  c (+ c  1)) )
      ( (setq l nil) )
    )
  )
  c
)

[Marc'Antonio Alessi]

Code: [Select]

-- Benchmark utility: In memory of Michael Puckett ---

List length: 7
Elapsed milliseconds / relative speed for 131072 iteration(s):
    (LEE_F3 SMALLLIST)....................1500 / 1.86 <fastest>
    (LEE_F1 SMALLLIST)....................1547 / 1.81
    (GILE_LEN SMALLLIST)..................1578 / 1.77
    (MY-COUNT-LIST-STEF3 SMALLLIST).......1640 / 1.71
    (TH_LENGTH_ SMALLLIST)................1672 / 1.67
    (APR_LENGTH SMALLLIST)................1687 / 1.66
    (ALE_LENGTH SMALLLIST)................1906 / 1.47
    (MY-COUNT-LIST-SE7EN SMALLLIST).......2281 / 1.23
    (MY-COUNT-LIST-STEFONE SMALLLIST).....2734 / 1.02
    (LENGTH-DEXUS SMALLLIST)..............2797 / 1 <slowest>

List length: 82
Elapsed milliseconds / relative speed for 65536 iteration(s):
    (ALE_LENGTH MEDIUMLIST)................1063 / 2.45 <fastest>
    (LEE_F3 MEDIUMLIST)....................1094 / 2.38
    (LEE_F1 MEDIUMLIST)....................1656 / 1.58
    (GILE_LEN MEDIUMLIST)..................1765 / 1.48
    (MY-COUNT-LIST-STEFONE MEDIUMLIST).....1937 / 1.35
    (LENGTH-DEXUS MEDIUMLIST)..............1938 / 1.35
    (MY-COUNT-LIST-STEF3 MEDIUMLIST).......2172 / 1.2
    (MY-COUNT-LIST-SE7EN MEDIUMLIST).......2344 / 1.11
    (TH_LENGTH_ MEDIUMLIST)................2594 / 1.01
    (APR_LENGTH MEDIUMLIST)................2609 / 1 <slowest>

List length: 4100
Elapsed milliseconds / relative speed for 8192 iteration(s):
    (ALE_LENGTH BIGLIST)................1828 / 4 <fastest>
    (LEE_F3 BIGLIST)....................3094 / 2.36
    (LENGTH-DEXUS BIGLIST)..............3938 / 1.86
    (MY-COUNT-LIST-STEFONE BIGLIST).....3969 / 1.84
    (LEE_F1 BIGLIST)....................6688 / 1.09
    (GILE_LEN BIGLIST)..................7312 / 1 <slowest>

List length: 4198400
Elapsed milliseconds / relative speed for 8 iteration(s):
    (ALE_LENGTH ULTRALIST)................1015 / 3.71 <fastest>
    (LEE_F3 ULTRALIST)....................2344 / 1.61
    (LENGTH-DEXUS ULTRALIST)..............3687 / 1.02
    (MY-COUNT-LIST-STEFONE ULTRALIST).....3765 / 1 <slowest>


[Marc'Antonio Alessi]

Code: [Select]

; "strange" version - length <= 100
(defun ALE_LengthNth (L)
  (nth 100 (append L
   '( 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80
      79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59
      58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38
      37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17
      16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
    )
  )       )
)