Re: Sorting atoms in a case-insensitive manner?

From: Jan Wielemaker (jan_at_ct.xs4all.nl)
Date: 11/29/03

  • Next message: Bart Demoen: "Re: Sorting atoms in a case-insensitive manner?" 
    Date: 29 Nov 2003 14:26:59 GMT

    In article <pan.2003.11.29.11.28.11.885516@in.signature>, seguso wrote:
    >
    > Is there any easy way to sort a list of atoms in a case-insensitive manner?
    >
    > predsort(compare, List, SortedList).
    >
    > sorts it like that:
    >
    > Aaaa
    > BBbbb
    > aaaa
    > bbbb
    >
    > whereas I need
    >
    > Aaaa
    > aaaa
    > BBbbb
    > bbbb
    >
    > Thanks for your kind help.

    Not really. As you are using SWI-Prolog anyway, the fastest definition
    is:

    case_insensitive_sort(Atoms, Sorted) :-
            key_case(Atoms, Keyed),
            keysort(Keyed, Sorted0),
            unkey(Sorted0, Sorted).

    key_case([], []).
    key_case([H|T0], [L-H|T]) :-
            downcase_atom(H, L),
            key_case(T0, T).

    unkey([], []).
    unkey([_-T0], T) :-
            unkey(T0, T).

    (not tested).

    I've considered adding a built-in as this operation is quite common in
    some application domains and a built-in avoids the creation of a large
    number of garbage atoms.

            --- Jan

  • Next message: Bart Demoen: "Re: Sorting atoms in a case-insensitive manner?"

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