Tricky sorting

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From	"WJ" <w_a_x_man@yahoo.com>
Newsgroups	comp.lang.forth
Subject	Tricky sorting
Date	Thu, 14 Jul 2016 06:13:45 -0000 (UTC)
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You have a list of pairs.  After sorting, if you look only
at the first element of each pair, it should seem that
nothing has changed.

Example.  (Since we're temporarily ignoring the second
elements, they're represented by underscores.)

Before:
[(5,_); (5,_); (2,_); (2,_)]

After:
[(5,_); (5,_); (2,_); (2,_)]

However, the list should be ordered by the second elements,
in so far as that can be done without changing the order of
the first elements.

Before:
[(5,8); (5,0); (2,6); (2,3)]

After:
[(5,0); (5,8); (2,3); (2,6)]



OCaml:

List.sort
  (fun (a,b) (c,d) -> if a=c then compare b d else 0)
  [3,5; 3,1; 3,3; 1,2; 1,7; 1,1; 888,9; 3,42; 3,0] ;;5

 ===>
[(3, 1); (3, 3); (3, 5); (1, 1); (1, 2); (1, 7); (888, 9); (3, 0); (3, 42)]


For this task, or any task not trivially simple, why would one
want to use ANS Forth, a language lacking sorting, lists, arrays,
tuples, and just about everything else?


-- 
Amazon bans book.  After nearly a month on the site, all traces of the book and
its 80 reviews have been removed.
http://jamesfetzer.blogspot.com/2015/11/debunking-sandy-hook-debunkers-5.html
https://www.youtube.com/watch?v=EEl_1HWFRfo

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Tricky sorting "WJ" <w_a_x_man@yahoo.com> - 2016-07-14 06:13 +0000
  Re: Tricky sorting "WJ" <w_a_x_man@yahoo.com> - 2016-07-14 06:25 +0000
  Re: Tricky sorting "WJ" <w_a_x_man@yahoo.com> - 2016-07-14 06:44 +0000
    Re: Tricky sorting Richard Todd <richard.wesley.todd@gmail.com> - 2016-07-14 14:56 -0700

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