I have a 2 dimensional array like this:
$map[0][0] = 'a';
$map[0][1] = 'b';
$map[1][0] = 'c';
$map[1][1] = 'd';
I want to pass only everything under $map[1] (by reference) to a subroutine. How to do that ?
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3 Answers
Perl doesn't have multiple dimension arrays.
What you have is an array and each element of that array is a reference to another array. You might want to read up about Perl References since this is the way Perl allows you to build some very complex data structures.
Many people think of it as a multidimensional array, and you could treat it as such under certain circumstances. However, I prefer the -> syntax which reminds me that this is merely a reference to a reference.
$map[0]->[0] = 'a';
$map[0]->[1] = 'b';
$map[1]->[0] = 'c';
$map[1]->[1] = 'd';
Now, I can take the data structure apart:
@map: This is an array with two items in it,$map[0]and$map[1].$map[0]->[]: This is a reference to another array. That array also has to items in it.$map[1]->[]: This is another reference to yet another array. That array has two items in it.
Note that $map[1]->[] means that $map[1] contains an array reference. Thqt means you can pass $map[1] as your reference to that inner array.
mysub ($map[1]);
Here's a simple program:
#! /usr/bin/env perl
#
use strict;
use warnings;
use feature qw(say);
my @map;
$map[0]->[0] = 'a';
$map[0]->[1] = 'b';
$map[1]->[0] = 'c';
$map[1]->[1] = 'd';
mysub( $map[1] );
sub mysub {
my $array_ref = shift;
my @array = @{ $array_ref }; # Dereference your reference
for my $index ( 0..$#array ) {
say "\$map[1]->[$index] = $array[$index]";
}
}
This prints:
$map[1]->[0] = c
$map[1]->[1] = d
Now, you see why I like that -> syntax although it's really completely unnecessary. It helps remind me what I am dealing with.
Comments
You can send array reference,
sub mysub {
my ($aref) = @_;
# work with @$aref ..
}
mysub($map[1]);
Comments
Simply pass the scalar $map[1].
fn($map[1]);
sub fn
{
my @loc_map_1 = @{ $_[0] };
Remember that perl doesn't have "real" 2 dimensional arrays. In your case map is an array that contains 2 references to arrays.
