28 lines
621 B
Prolog
28 lines
621 B
Prolog
% transposition of a rectangular matrix
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% e.g. [[1,2,3,4], [5,6,7,8]]
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% give [[1,5],[2,6],[3,7],[4,8]]
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transpose(In, Out) :-
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In = [H | T],
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maplist(initdl, H, L),
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work(T, In, Out).
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% we use the difference list to make "quick" appends (one inference)
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initdl(V, [V | X] - X).
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work(Lst, [H], Out) :-
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maplist(my_append_last, Lst, H, Out).
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work(Lst, [H | T], Out) :-
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maplist(my_append, Lst, H, Lst1),
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work(Lst1, T, Out).
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my_append(X-Y, C, X1-Y1) :-
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append_dl(X-Y, [C | U]- U, X1-Y1).
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my_append_last(X-Y, C, X1) :-
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append_dl(X-Y, [C | U]- U, X1-[]).
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% "quick" append
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append_dl(X-Y, Y-Z, X-Z).
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