Turn a list into a matrix

Question

I worked all afternoon on a simple thing but cannot seem to get it right for some reason : how to turn a list into a matrix of given width.

Example : I got a list such a

Answer 1

BTW, I thought I'd mention the code I finally wrote :

length_(Length, List) :- length(List, Length).

list2matrix(List, RowSize, Matrix) :-
    length(List, L),
    HowManyRows is L div RowSize,
    length(Matrix, HowManyRows),
    maplist(length_(RowSize), Matrix),
    append(Matrix, List).

It's more high order oriented and funnier to read I guess :)