[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: remove sublist

From: Emanuel Berg
Subject: Re: remove sublist
Date: Mon, 02 Apr 2018 15:28:57 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux)

Yuri Khan wrote:

> Maybe
>     (cl-set-difference '("0" "a" "b" "c" "d")
>                        '("a" "b")
>                        :test 'string=)
> ?

Excellent, thanks!

You got the right idea, "sublist" as in the
math unordered set sense - and not "set" as in
the serpent god of the paleo-pharaohs, here!

And items in the sublist that do not appear
should be dropped, as happens.

Should the test function be hash-quoted?

Only strange thing is the order is reversed,
except for the empty list as sublist! I just
said it was in the unordered sense, however one
might just as well keep the order, especially
since even/particularly in the math unordered
set sense, {1 2 3} = {3 2 1}, right? So it
should work both ways; and it might be useful
for example if you have a list of functions,
(f1 f2 f3 f4), and it is a priority list so if
f1 is defined, run it, if not, try/run f2,
etc., here, if the user dislikes f2 and f3, but
have them defined for other purposes, s/he can
remove them from the list without changing
the priority!

However how is that supposed to be done?
What about

    (defun drop-sublist (l sl)
      (if sl
          (reverse (cl-set-difference l sl :test #'string-equal))
    ;; (drop-sublist '("0" "a" "b" "c" "d") '("a" "b" "x"))
    ;; (drop-sublist '("0" "a" "b" "c" "d") '(x))
    ;; (drop-sublist '("0" "a" "b" "c" "d") '())


It sort of goes against grain to reverse to
*preserve* the order, but I suppose this is
what makes programming an engineering and not
a scientific endeavor...

underground experts united

reply via email to

[Prev in Thread] Current Thread [Next in Thread]