Topic: How to check if coordinates are equal ?

[Coder]

Hello .

I would like to check if a coordinate is a member in a list .

Code: [Select]

  (setq mylist (23.337 6.63198) (22.9351 6.23005) (22.9351 8.02967) (16.5646 12.593) (14.5698 8.22248) (9.64711 7.83685) (6.42968 11.661) (6.42968 5.65161))

this code fail >>>>
(mapcar (function (lambda (coord)
  (if (member '(23.337 6.63198) coord)
    (setq num (1+ num))
    )))
    mylist
  )
and this one also >>>>

(mapcar (function (lambda (coord)
  (if (vl-position '(23.337 6.63198) coord)
    (setq num (1+ num))
    )))
    mylist
  )

Thanks

[dgorsman]

Coordinates may have additional numbers past the displayed precision, so unlike definite information (e.g. "a" always matches "a") its very difficult to get an exact match out of a list with (member...), (vl-position...), etc. which by default do an (= ...) type check which requires an exact match.

Consider rolling your own comparison function using (equal...) so you can specify a fuzz-factor.

[gile]

Hi,

Code: [Select]

(defun gc:memberFuzz (expr lst fuzz)
  (while (and lst (not (equal (car lst) expr fuzz)))
    (setq lst (cdr lst))
  )
  lst
)

[Keith™]

+1 on the roll yer own and "equal"

In your lambda function, try comparing the X and Y coords independently using a fuzz factor

Code: [Select]

(and (equal 23.337 (car coord) 0.0001)(equal 6.63198 (cadr coord) 0.0001))


[Lee Mac]

Code - Auto/Visual Lisp: [Select]

1. (defun MemberWithFuzz ( itm lst fuzz )
2.     (vl-member-if '(lambda ( x ) (equal x itm fuzz)) lst)
3. )

[Coder]

Thank you all guys .

What is the best value for fuzz ?

[MP]

peach

[Coder]

peach

peach has a value ?

[fixo]

0.00001 would be enough for your list

[dgorsman]

I generally aim for one decimal place smaller than the most precise number e.g. coordinates are in millimeters, I would use a fuzz factor of 0.1 (mm).  If coordinates are in meters to three decimal places i.e. m.mmm I would use 0.0001 (m).

[Kerry]

Thank you all guys .

What is the best value for fuzz ?

Bill's beard.



sorry, you probably had to be there

[Coder]

Thank you all guys .

What is the best value for fuzz ?

Bill's beard.

sorry, you probably had to be there

Hi Kerry .

I have no idea about that , can you please be more straight to the point . ? 

Thank you

[Coder]

I am sorry guys , I am still don't know how to chose the correct value for the fuzz and how to filter a list of coordinates to
remove the equal one from the list. 

Thanks

[Stefan]

Remove a point from a list:

Code - Auto/Visual Lisp: [Select]

1. (defun remove_point (point lst)
2.   (if (equal point (car lst) 1e-4)
3.     (cdr lst)
4.     (if lst (cons (car lst) (remove_point point (cdr lst))))
5.     )
6.   )
7.  

Code: [Select]

_$ (setq mylist '((23.337 6.63198) (22.9351 6.23005) (22.9351 8.02967) (16.5646 12.593) (14.5698 8.22248) (9.64711 7.83685) (6.42968 11.661) (6.42968 5.65161)))
_$ (remove_point '(16.5646 12.593) mylist)
((23.337 6.63198) (22.9351 6.23005) (22.9351 8.02967) (14.5698 8.22248) (9.64711 7.83685) (6.42968 11.661) (6.42968 5.65161))A precision of 1e-4 would be enough.

[Stefan]

Previous lisp will remove only first instance of a point from a list of points.
To remove all points, use this

Code - Auto/Visual Lisp: [Select]

1. (defun remove_point (point lst)
2.   (if lst
3.     (if (equal point (car lst) 1e-4)
4.       (remove_point point (cdr lst))
5.       (cons (car lst) (remove_point point (cdr lst)))
6.       )
7.     )
8.   )