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Re: Sorting in-place
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From:
merlyn
Date:
July 25, 2001 17:05
Subject:
Re: Sorting in-place
Message ID:
m1wv4wd07k.fsf@halfdome.holdit.com
>>>>> "Clinton" == Clinton A Pierce <clintp@geeksalad.org> writes:
Clinton> @dummy=sort {
Clinton> $r=$a cmp $b;
Clinton> if ($r < 0) {
Clinton> ($a,$b)=($b,$a);
Clinton> $r=1;
Clinton> }
Clinton> $r;
Clinton> } @list;
Clinton> # Is @list sorted? Not quite...
Clinton> Except this doesn't work. Oh, $a and $b get modified and they're swapped
Clinton> at appropriate times, but the resulting mess in @list can hardly be called
Clinton> proper ordering.
For this to work, the element indirected by $a would have to always be
to the left of the element indirected by $b, and that's probably not
true. In fact, we can see this:
@dummy = sort {
print "$a $b\n";
$a <=> $b;
} 1..9;
4 5
5 6
3 5
2 5
1 5
5 7
5 8
5 9
7 6
8 7
9 8
2 1
3 2
4 3
See the last few? If you were to swap the 4/3 pair to put them
in order, you're actually taking them *out* of order.
--
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<merlyn@stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
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