The different results obtained by apply function.

The different results obtained by apply function.

[Hongyi Zhao]

I try to reproduce the results given here [1], as follows:

(mapcar 'list '((1 2)(3 4))) ;; (((1 2)) ((3 4)))

(funcall 'mapcar 'list '((1 2)(3 4))) ;; (((1 2)) ((3 4)))

(apply 'mapcar 'list '((1 2)(3 4)) ()) ;; (((1 2)) ((3 4)))

The last one is different from the one given on the URL above:

(apply 'mapcar 'list '((1 2)(3 4))) ;; ((1 3) (2 4))

[1] https://stackoverflow.com/a/68876647

Any hints for this?
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

Re: The different results obtained by apply function.

[Michael Heerdegen]

Hongyi Zhao <hongyi.zhao@gmail.com> writes:

> The last one is different from the one given on the URL above:
>
> (apply 'mapcar 'list '((1 2)(3 4))) ;; ((1 3) (2 4))

That gives an error with Emacs Lisp - but please try with `cl-mapcar'.
Is that enough as hint?

Michael.

Re: The different results obtained by apply function.

[Hongyi Zhao]

On Thu, Oct 7, 2021 at 1:42 PM Michael Heerdegen
<michael_heerdegen@web.de> wrote:
>
> Hongyi Zhao <hongyi.zhao@gmail.com> writes:
>
> > The last one is different from the one given on the URL above:
> >
> > (apply 'mapcar 'list '((1 2)(3 4))) ;; ((1 3) (2 4))
>
> That gives an error with Emacs Lisp - but please try with `cl-mapcar'.
> Is that enough as hint?

Yep.

(apply 'cl-mapcar 'list '((1 2)(3 4))) ;; ((1 3) (2 4))

HZ

Re: The different results obtained by apply function.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> Yep.
>
> (apply 'cl-mapcar 'list '((1 2)(3 4))) ;; ((1 3) (2 4))

You can get this effect without `apply' with `cl-mapcar', and
the usual `mapcar' behavior without cl-mapcar:

  (cl-mapcar #'list       '(1 2) '(3 4))  ; ( (1 3)   (2 4))
  (cl-mapcar #'list (list '(1 2) '(3 4))) ; (((1 2)) ((3 4)))
     (mapcar #'list (list '(1 2) '(3 4))) ; (((1 2)) ((3 4)))

-- 
underground experts united
https://dataswamp.org/~incal

Re: The different results obtained by apply function.

[Emanuel Berg via Users list for the GNU Emacs text editor]

> You can get this effect without `apply' with `cl-mapcar',
> and the usual `mapcar' behavior without cl-mapcar:
>
>   (cl-mapcar #'list       '(1 2) '(3 4))  ; ( (1 3)   (2 4))
>   (cl-mapcar #'list (list '(1 2) '(3 4))) ; (((1 2)) ((3 4)))
>      (mapcar #'list (list '(1 2) '(3 4))) ; (((1 2)) ((3 4)))

While it is easy to say `cl-mapcar' is much cooler with the
aggregate function over multiple sets ... but observe

  (cl-mapcar #'list '(1 2) '(3 4))   ; ((1 3) (2 4))
  (cl-mapcar #'list '(1 2) '(3 4 5)) ; ((1 3) (2 4))

so same outdata for different indata - non-injective!

-- 
underground experts united
https://dataswamp.org/~incal