OpenEuphoria

RE: stable sorting

• Posted by rforno at tutopia.com Feb 27, 2003
• 435 views

Juergen:
I have not tested it, but I think that substituting "compare" by a
"custom_compare" in all places where "compare" appears will do the trick.
For an example, please look at my diff package.
Best regards.




----- Original Message -----
From: Juergen Luethje <eu.lue at gmx.de>
Subject: stable sorting


>
> I wrote:
>
> > Subject: Re: Euphoria 2.4 Alpha-test Release!
>
> [...]
> > 5) Documentation of sort():
> >    Nothing special with version 2.4, I just came across it.
> >    I think it would be valuable to mention, whether or not the sorting
> >    of sort() is stable, along with a short explanation for beginners,
> >    what that means.
> [...]
>
> Probably I should have been somewhat more specific. I actually was
> thinking more of custom_sort(), than of sort():
> Say I have a list of records with student names and marks, already
> sorted by name. Then i want to sort this list by mark, so that students
> with the same mark remain listed in alphabetical order.
>
> The following code (modified after 'csort.ex') does *not* perform a
> stable sorting.
>
> ----------=----------=----------=----------=----- begin of code
> include sort.e
>
> constant MARK = 2
> constant statistics = {
>    {"Doe", 3},
>    {"Einstein", 1},
>    {"Goldberg", 1},
>    {"Irving", 4},
>    {"Jones", 3},
>    {"Miller", 2},
>    {"Neuman", 2},
>    {"Petersen", 4},
>    {"Smith", 2},
>    {"Zander", 5}
> }
>
> function compare_mark (sequence a, sequence b)
>    -- Compare two sequences (records) according to MARK.
>    return compare(a[MARK], b[MARK])
> end function
>
> integer by_mark
> sequence sorted_by_mark
>
> by_mark  = routine_id("compare_mark")
> sorted_by_mark = custom_sort(by_mark, statistics)
>
> puts(1, "sorted by mark\n\n")
> for i = 1 to length(sorted_by_mark) do
>    printf(1, "%12s %d\n", sorted_by_mark[i])
> end for
> ----------=----------=----------=----------=----- end of code
>
> Is there a library in the archive, with which this can be achieved?
> I didn't find one.
>
> Ricardo, I saw that your functions GradeDown() and GradeUp() in
> 'genfunc.e' perform stable sorting. But given the above example, there
> is no way to tell them just to sort by mark, and not to compare the
> whole records, right?
>
>
> Best regards,
>    Juergen
>
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