Re: Problem in Passing A Multidimensional Array into a Function

Perl doesn't talk about "pointers", it uses "references". It doesn't have multi-dimensional arrays, Perl has arrays of references (each of which may be to an array). Perl always passes parameters to subs by reference.

If you want a temporary copy of a complicated data structure (that is really pretty much anything using references) you need to make a "deep copy". Perl doesn't have an inbuilt way to do that, but there are a number of modules that do the trick. Most common is Storable. Consider:

use strict;
use warnings;
use Storable;
use Data::Dump::Streamer;

my $ref = [
    {a => 1, b => 2, c => 3},
    [1, 2, 3],
    {x => [4, 5, 6], y => [7, 8, 9]},
    ];

my $org = Dump ($ref)->Out ();

mangle ($ref);

my $after = Dump ($ref)->Out ();

print "Structure unmangled" if "$org" eq "$after";


sub mangle {
    my $cloned = Storable::dclone ($_[0]);
    
    $cloned->[0]{a} = 6;
    $cloned->[1][0] = 23;
    
    Dump $cloned;
}
[download]

Prints:

$ARRAY1 = [
            {
              a => 6,
              b => 2,
              c => 3
            },
            [
              23,
              2,
              3
            ],
            {
              x => [
                     4,
                     5,
                     6
                   ],
              y => [
                     7,
                     8,
                     9
                   ]
            }
          ];
Structure unmangled
[download]

Perl reduces RSI - it saves typing

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Re^2: Problem in Passing A Multidimensional Array into a Function by smiffy (Pilgrim) on Oct 02, 2008 at 02:25 UTC
Here is an example of a deep copy, for reference. Note that this is not efficient - you'd be better off using a module as GrandFather suggests. (Modules are great for getting things done, but don't always show you how they are doing them.) `my @a1; # First array # Pretend we're putting something in the first array. my @a2=aoacpy(@a1); sub aoacpy { my @array_in=@_; my @array_out; # Iterate through parent array. for (my $i=0; $i<scalar(@array_in); $i++) { # Iterate through child array - note that # we do this for each member of the parent # array. for (my $j=0; $j<scalar($array_in[$i]); $j++) { $array_out[$i][$j]=$array_in[$i][$j]; } } return @array_out; }` [download] I'm now scratching my head trying to work out why this is so slow - it shouldn't be iterating that many times.	[reply] [d/l]

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Re^2: Problem in Passing A Multidimensional Array into a Function
by smiffy (Pilgrim) on Oct 02, 2008 at 02:25 UTC

Here is an example of a deep copy, for reference. Note that this is not efficient - you'd be better off using a module as GrandFather suggests. (Modules are great for getting things done, but don't always show you how they are doing them.)

my @a1; # First array

# Pretend we're putting something in the first array.

my @a2=aoacpy(@a1);

sub aoacpy
{
  my @array_in=@_;
  my @array_out;
  # Iterate through parent array.
  for (my $i=0; $i<scalar(@array_in); $i++)
  {
    # Iterate through child array - note that 
    # we do this for each member of the parent 
    # array.
    for (my $j=0; $j<scalar($array_in[$i]); $j++)
    {
      $array_out[$i][$j]=$array_in[$i][$j];
    }
  }
  return @array_out;
}
[download]

I'm now scratching my head trying to work out why this is so slow - it shouldn't be iterating that many times.

[reply]
[d/l]