On Wed, 12 Apr 2017 18:16:56 -0400
Uri Guttman <u...@stemsystems.com> wrote:
> On 04/12/2017 05:42 PM, Shawn H Corey wrote:
> > On Wed, 12 Apr 2017 16:19:32 -0400
> > Uri Guttman <u...@stemsystems.com> wrote:
> >
> >
> > my @array;
> >
> > for my $index (reverse sort @indices) {
> >> sort defaults to a lexical sort which won't work well on integers
> >> with more than 2 digits.
> >>
> >> and why are you sorting and reversing the indexes? i don't think
> >> that will help make the splice more efficient if any of the
> >> indexes are not at the end of the array.
> > If you're going to splice, do it from the highest index to the
> > lowest. Otherwise the splice will shift the end of the array down,
> > which messes up the indexing.
> but if the splice is not at the end of the array it doesn't save
> much. you still have to shift down multiple elements on each call to
> splice. maybe you shift down fewer as there are now fewer elements up
> top. anyhow, i was somewhat surprised to see splice was the fastest
> method. i feel there is something odd and maybe with a larger data
> set, that wouldn't be the case.
>
> uri
>
It's not about saving time. It's about removing a bug. In the code
below, notice that there are two different outputs depending on the
order that splice is applied. It's only by using descending indexing do
you get the correct deletions.
#!/usr/bin/env perl
use strict;
use warnings;
say "ascending indexing";
my @a = 'a' .. 'z';
say "@a";
splice( @a, 3, 1 );
say "@a";
splice( @a, 9, 1 );
say "@a";
say "descending indexing";
@a = 'a' .. 'z';
say "@a";
splice( @a, 9, 1 );
say "@a";
splice( @a, 3, 1 );
say "@a";
__END__
ascending indexing
a b c d e f g h i j k l m n o p q r s t u v w x y z
a b c e f g h i j k l m n o p q r s t u v w x y z
a b c e f g h i j l m n o p q r s t u v w x y z
descending indexing
a b c d e f g h i j k l m n o p q r s t u v w x y z
a b c d e f g h i k l m n o p q r s t u v w x y z
a b c e f g h i k l m n o p q r s t u v w x y z
--
Don't stop where the ink does.
Shawn H Corey
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