Array slicing through a reference: Inefficient?

[Ethan Brown]

Dear Group--

I'm working on a project where I'm working with large arrays, and I'm
using references to pass arrays around to reduce memory use as much as
possible. I often work with small subsets of a referenced array and
access it like:

my @subrange = @{$big_array_ref}[$start_idx .. $end_idx];

Also, to get the array size, I'll do:

my $num_points = @$big_array_ref;

Is this the best practice? Do I need to be concerned in a statement
like

@{$big_array_ref}[$start_idx .. $end_idx];

that the array referenced by $big_array_ref is being completely copied
before the subrange is taken? Likewise for the $num_points example.

Thanks,

--Ethan Brown
--Keyboards: "The Fabulous Pelicans" ([url]www.pelicans.com[/url])
--In a band? Use [url]http://www.WheresTheGig.com[/url] for free.

[Tassilo v. Parseval]

Also sprach Ethan Brown:

> I'm working on a project where I'm working with large arrays, and I'm
> using references to pass arrays around to reduce memory use as much as
> possible. I often work with small subsets of a referenced array and
> access it like:
>
> my @subrange = @{$big_array_ref}[$start_idx .. $end_idx];
>
> Also, to get the array size, I'll do:
>
> my $num_points = @$big_array_ref;
>
> Is this the best practice? Do I need to be concerned in a statement
> like
>
> @{$big_array_ref}[$start_idx .. $end_idx];
>
> that the array referenced by $big_array_ref is being completely copied
> before the subrange is taken? Likewise for the $num_points example.

There is no need to worry here. If you have a reference to an array,
this means that the actual array also exists somewhere and you just
happen to access it through a reference. You're not duplicating any
arrays and no temporary huge arrays are built either.

Tassilo
--
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[pkent]

In article <vr1xufl44l.fsf@draupnir.gso.saic.com>,
Ethan Brown <ethan@draupnir.gso.saic.com> wrote:

> Is this the best practice? Do I need to be concerned in a statement
> like
>
> @{$big_array_ref}[$start_idx .. $end_idx];
>
> that the array referenced by $big_array_ref is being completely copied
> before the subrange is taken? Likewise for the $num_points example.

As far as I know - but I haven't read the friendly source - the array is
not copied. In other words you're saying to perl "give me the slice
$start to $end from the array _pointed to_ by $arrayref". So I'd say to
you: don't worry , I think you're doing things the right way

P

--
pkent 77 at yahoo dot, er... what's the last bit, oh yes, com
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