CODEWITHSUNDEEP
prolog
Aizzaac
Aizzaac

Reputation: 3318

How to extract the columns form a matrix and use them in another predicate, in prolog?

I want to use the results from "extract" (W) in valid_seq which is then use in valid_columns.

I have tried this so far, but it does not work: 

extract(_,[],[]).
extract(K,[X|Y],[H|L]) :- nth1(K,X,H), extract(K,Y,L).

valid_columns([],[]).
valid_columns([H|L],[X|Y],K) :- b_w(X),
                extract(K,X,W), 
                valid_seq(H,W),
                K1 is K+1,
                valid_columns(L,Y,K1).

EDIT:

I am trying to solve a nonogram. So from each list of lines, I have to extract the columns to validate them. This is the function "extract"

Once the columns are extracted I need to validate them. Ex

valid_column([[1,1,1,1,1],[1,0,0,0,0],[1,1,1,1,1],[0,0,0,0,1],[1,1,1,1,1]],[3,1],1).
false.

Here I am asking if the first value in each [] complies to [3,1]. In this case should be true. As I have [1 1 1 0 1].

And this is my code:

test_cst(0,[0|S],S).   
test_cst(0,[],[]). 
test_cst(N,[1|T],S):- 
                    N1 is N-1,
                    test_cst(N1,T,S).

valid_seq([],[]).      
valid_seq(L,[0|T]):-valid_seq(L,T).      

valid_seq([H|L],[1|T]):-test_cst(H,[1|T],S),valid_seq(L,S). 

b_w([]).
b_w([H|L]) :- H is 0, b_w(L);H is 1, b_w(L).

valid_lines([],[]).
valid_lines([H|L],[X|Y]) :- b_w(X), 
                            valid_seq(H,X),
                            valid_lines(L,Y).


extract(_,[],[]).
extract(K,[X|Y],[H|L]) :- nth1(K,X,H), extract(K,Y,L).

valid_columns([],_,_).
valid_columns([H|L],X,K) :- valid_column(X,H,K),
                            K1 is K+1,
                            valid_columns(L,X,K1).

valid_column(X,H,K) :- b_w(X),
                       extract(K,X,W), 
                       valid_seq(H,W).

Upvotes: 0

Views: 264

Answers (1)

CapelliC
CapelliC

Reputation: 60034

If available, you can put library(apply) to good use:

?- maplist(nth1(I), [[a,b,c],[1,2,3],[x,y,z]], X).
I = 1,
X = [a, 1, x] ;
...

I'm suggesting its usage since it simplifies the code, removing irrelevant details, that blurry your relations.

For your question, you're passing to b_w/1 a list of lists, while it should be a list. If you have library(yall) available, b_w/1 can be rewritten like

b_w(L) :- maplist([X]>>(X=0;X=1), L).

Upvotes: 1

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