Author Topic: (Challenge) Closest integer to n  (Read 7383 times)

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Mark

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(Challenge) Closest integer to n
« on: March 11, 2005, 08:35:01 AM »
Write a function that returns the closest integer to n given a list of integers.

Example:
Code: [Select]

(setq lst '(45 23 63 5 8 56 74 32 96 144 95))

return the number closest to 10;
answer = 8.

Have fun. :D
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MP

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(Challenge) Closest integer to n
« Reply #1 on: March 11, 2005, 09:14:23 AM »
Oops.
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whdjr

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(Challenge) Closest integer to n
« Reply #2 on: March 11, 2005, 10:13:25 AM »
Rules? 8)

Mark

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(Challenge) Closest integer to n
« Reply #3 on: March 11, 2005, 10:27:41 AM »
Quote from: whdjr
Rules?

Nope!! Go for it, let's see what ya got. :D

commence posting, post at will..............
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whdjr

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(Challenge) Closest integer to n
« Reply #4 on: March 11, 2005, 10:38:06 AM »
Quote from: Mark Thomas
commence posting, post at will..............

NO! NO! NOT AT ME!   :lol:  :lol:

Seriously.

Here's mine:
Code: [Select]
(setq lst '(45 23 63 5 8 56 74 32 96 144 95))

(defun closest (nlst / int pos)
  (initget (+ 1 4))
  (setq int (getint "\nEnter a number: "))
  (setq pos (vl-position
     0
     (vl-sort-i (mapcar '(lambda (n) (abs (- n int))) nlst) '>)
   )
  )
  (princ (strcat "The number closest to "
(itoa int)
" is "
(itoa (nth pos nlst))
"."
)
  )
)

whdjr

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(Challenge) Closest integer to n
« Reply #5 on: March 11, 2005, 11:50:29 AM »
Here's one that works with negatives as well:
Code: [Select]
(setq lst2 '(-45 -23 -63 5 -8 56 74 32 -96 -144 95))

(defun closest2 (nlst / int pos)
  (initget 1)
  (setq int (getint "\nEnter a number: "))
  (setq pos (vl-position
     (apply 'min
    (setq pos (mapcar 'abs (mapcar '(lambda (n) (- n int)) nlst)))
     )
     pos
   )
  )
  (princ (strcat "The number closest to "
(itoa int)
" is "
(itoa (nth pos nlst))
"."
)
  )
)

CAB

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(Challenge) Closest integer to n
« Reply #6 on: March 11, 2005, 12:43:20 PM »
I came up with two versions.
Code: [Select]
;;  version one
(defun nearest (num lst / a)
  (foreach x lst
    (if (or (null a)
            (< (abs(- num x)) (car a))
        )
      (setq a (list (abs(- num x)) x))
    )
  )
  (cadr a)
)


and after some thought version 2
Code: [Select]
(defun nearest2 (num lst / a)
  (car (vl-sort lst '(lambda (x y) (< (abs(- num x)) (abs(- num y)) ))))
)
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Kerry

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Re: (Challenge) Closest integer to n
« Reply #7 on: February 02, 2010, 02:59:04 AM »
< ... >
and after some thought version 2
Code: [Select]
(defun nearest2 (num lst / a)
  (car (vl-sort lst '(lambda (x y) (< (abs(- num x)) (abs(- num y)) ))))
)

That is SO pretty !!
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ElpanovEvgeniy

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Re: (Challenge) Closest integer to n
« Reply #8 on: February 02, 2010, 03:46:55 AM »
so there is less computation
Code: [Select]
(defun test (n l)
 (nth (car (vl-sort-i (mapcar '(lambda (a) (abs (- n a))) l) '<)) l)
)
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Joe Burke

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Re: (Challenge) Closest integer to n
« Reply #9 on: February 02, 2010, 06:17:21 AM »
Seems to me this could return zero or two. IOW, both answers are correct within context.

Command: (nearest2 1 '(0 2 3))
0

CAB

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Re: (Challenge) Closest integer to n
« Reply #10 on: February 02, 2010, 08:08:09 AM »
Thanks Kerry.

As always very nice Evgeniy.

That appears to be correct Joe.
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Joe Burke

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Re: (Challenge) Closest integer to n
« Reply #11 on: February 02, 2010, 10:28:31 AM »
I would probably use a genric function like this.

(defun round (value to)
  (if (zerop to) value
    (* (atoi (rtos (/ (float value) to) 2 0)) to)))

It works works with integer or real values passed. Plus it's numerically correct rounding. Not a qurirk of code rounding.

Lee Mac

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Re: (Challenge) Closest integer to n
« Reply #12 on: February 02, 2010, 10:46:21 AM »
I think Evgeniy has put this one to bed  :wink:

VovKa

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Re: (Challenge) Closest integer to n
« Reply #13 on: February 02, 2010, 11:27:22 AM »
ugly but should be the fastest in most cases
Code: [Select]
(defun nearest133 (num lst / a b c)
  (setq b (car lst)
a (abs (- num b))
  )
  (while (setq lst (cdr lst))
    (if (< (setq c (abs (- num (car lst)))) a)
      (setq b (car lst)
    a c
      )
    )
  )
  b
)

Lee Mac

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Re: (Challenge) Closest integer to n
« Reply #14 on: February 02, 2010, 01:35:40 PM »
Late entry, really just a modification of Will's   :-P

Code: [Select]
(defun Closest-LEEMAC (num lst / vlst)
  (nth
    (vl-position
      (apply (function min)
        (setq vlst
          (mapcar
            (function
              (lambda (x) (abs (- x num)))) lst))) vlst) lst))