Re: Sorting a list of lists in the order of ascending length

Markus Triska <[email protected]> Wed, 25 Sep 2013 14:40:13 +0200

Newsgroups	gmane.comp.ai.prolog.swi
Message-ID	<[email protected]>

Hi Norbert,

"Norbert E. Fuchs" <[email protected]> writes:

> I need all subsets of a list in the order of ascending length

What about:

   set_ascending_length_subset(Set, Sub) :-
           length(Set, N),
           between(0, N, L),
           length(Sub, L),
           phrase(subset(Set), Sub).

   subset([])     --> [].
   subset([L|Ls]) --> ( [L] ; []), subset(Ls).

Example:

   ?- findall(Sub, set_ascending_length_subset([a,b,c], Sub), Subs).
   %@ Subs = [[], [a], [b], [c], [a, b], [a, c], [b, c], [a|...]].

All the best,
Markus