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listprologcountingpredicates

Finding the most similar list from predicate knowledge base in Prolog

I have a problem in which I have a list of elements and I have to cycle through all instances of a particular /2 predicate to find which one has he highest number of matching elements in its list. In terms of implementation I can't seem to figure out how I should be updating the highest match so far and then stopping when there are no more.

findAnswer(MyList, HighMatchNum,_):-
    answer(X,Y),
    myIntersection(MyList, Y, NUM), //handles a single instance check and returns how many elements match.
    NUM > HighMatchNum,
    findAnswer(MyList, NUM, answer(X,Y)).

//Knowledge base
 answer(sample1, [a,b,c,d]).
 answer(sample2, [d,c,e]).
Solution

  • there is library(aggregate):

    findAnswer(MyList, HighMatchNum, K) :-
    aggregate_all(max(N, Key),
              (   answer(Key, List),
                  myIntersection(MyList, List, N)
              ),
              max(HighMatchNum, K)).

myIntersection(MyList, List, N) :-
    intersection(MyList, List, L),
    length(L, N).

% Knowledge base
answer(sample1, [a,b,c,d]).
answer(sample2, [d,c,e]).

    yields

    ?- findAnswer([a], C, K).
C = 1,
K = sample1.

?- findAnswer([d,e], C, K).
C = 2,
K = sample2.