cons list of points?

[M76]

Hi,

 

I'm trying to construct a list of points, but when I try to add a new element to the list with cons, the result is not what I expect.

 

Example:

list looks like this: ((50.0 40.0))

 

I have one point as a list in a list.

 

I try to add to the list with cons for example

 

(20.0 30.0)

 

I get this as a result:

 

(((20.0 30.0)) 50.0 40.0)

 

why?

[MSasu]

Use APPEND statement instead.

 

(setq List1st '((1 2) (3 4) (5 6) (7 ))
(setq List2nd '())

(foreach thePoint List1st 
(setq List2nd (append List2nd 
                      (list thePoint)))
)

 

Regards,

[Lee Mac]

I'm not sure of the desired result, but cons should return like this:

 

(cons '(20 30) '((40 50)))

==>  ((20 30) (40 50))

[David Bethel]

I think Lee's example is used lot more

 

( cons ) is a lot lot faster than ( append ) but it does make the final list in reverse order at times.

 

I use this a lot

 

(setq l1 '(40 50))

(setq l1 (cons '(20 30) l1)

(setq l1 (reverse l1))

 

-David

[Lee Mac]

Not really a conclusive test, but just as an example:

 

(defun cons-it nil
 (cons '(40 50) '((20 30))))

(defun append-it nil
 (append '((40 50)) '((20 30))))

 

(Benchmark '((cons-it) (append-it)))
Benchmarking ...................Elapsed milliseconds / relative speed for 65536 iteration(s):

   (CONS-IT).......1357 / 1.06 <fastest>
   (APPEND-IT).....1436 / 1.00 <slowest>

[M76]

I'm not sure of the desired result, but cons should return like this:

 

(cons '(20 30) '((40 50)))

==>  ((20 30) (40 50))

 

Yes it should but it does not. And I don't know why.

 

I can use append, speed is not an issue now.

[Lee Mac]

Yes it should but it does not. And I don't know why.

 

What code are you using?