Question

i’m having problems with this subject in Prolog.
The thing is that I want to count the number of repeated elements appearing in a list,
and I also want to fill, in another list with 1, for each appearance of duplicated elements and a 0 if is not duplicated, e.g.

I have a list like this: [420,325,420,582,135,430,582], and the result should be [1,0,1,1,0,0,1].

I’ve tried some code snippets and it’s driving me nuts.

The last code i’ve tried is:

count_duplicates([],[]).
count_duplicates([Head|Tail],[1|LS]):-
    member(Head,Tail),
    count_duplicates([Tail|Head],LS).

count_duplicates([Head|Tail],[0|LS]):-
    \+ member(Head,Tail),
    count_duplicates([Tail|Head],LS).

this predicate receive a list and have to generate the result list

Thanks in advance

Answer 1

You can try this :

count_duplicate(In, Out) :-
    maplist(test(In), In, Out).


test(Src, Elem, 1) :-
    select(Elem, Src, Result),
    member(Elem, Result).

test(_Src, _Elem, 0).

EDIT Without maplist, you can do

count_duplicate(In, Out) :-
    test(In, In, Out).

test(_, [], []).

test(In, [Elem | T], [R0 | R]) :-
    select(Elem, In, Rest),
    (   member(Elem, Rest) -> R0 = 1; R0 = 0),
    test(In, T, R).