CODEWITHSUNDEEP
listprolog
user3502598
user3502598

Reputation: 63

Splitting a list of numbers into a list of lists of pairs

Say I have a list [1, 2, 3, 4, 5, 6, 7, 8], what I want to do is have an output of [[1,2], [3,4], [5,6], [7,8]].

This is my current attempt at doing this:

perms([X,Y], [X,Y], _).
perms(L, R, N) :-
   N > 1,
   N1 is N/2,
   split(L, X1, X2),
   perms(X1, R1, N1),
   perms(X2, R2, N1),
   append([R1], [R2], R).

split(L, R1, R2) :-
   append(R1, R2, L),
   length(L, N),
   N1 is N/2,
   length(R1, N1),
   length(R2, N1).

Assume N is the length of the list that I will enter manually.

Upvotes: 2

Views: 1122

Answers (2)

Sergii Dymchenko
Sergii Dymchenko

Reputation: 7229

group([], []).
group([A, B | Tail], [[A, B] | NewTail]) :-
    group(Tail, NewTail).

Test run:

?- group([1, 2, 3, 4, 5, 6, 7, 8], X).
X = [[1, 2], [3, 4], [5, 6], [7, 8]].

?- group([1, 2, 3, 4, 5, 6, 7], X).
false.

?- group([], X).
X = [].

Upvotes: 3

CapelliC
CapelliC

Reputation: 60034

The answer seems too much simple, I'm fairly sure I didn't understand your requirement. Anyway, you could try

pairs([X,Y],[[X,Y]]).
pairs([X,Y|R],[[X,Y]|T]) :- pairs(R, T).

Upvotes: 3

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