different hash construction processes in Perl - perl

Question

I noticed a hash object was once defined as in the following:
my %data = ();
$data{file} = $file;
$data{concept} = $#row;
$data{line1} {$cell[0]} = $cell[1];
What does this hash construction process try to achieve? Or what is the difference between
$data{concept} = $#row;
and
$data{line1} {$cell[0]} = $cell[1];
?

Answer 1

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my $file = "contents of my file";
my #row = qw(some random data);
my #cell = qw(key value);
my %data = ();
$data{file} = $file;
$data{concept} = $#row;
$data{line1} {$cell[0]} = $cell[1];
print Dumper \%data;
Output:
$VAR1 = {
'file' => 'contents of my file',
'line1' => {
'key' => 'value'
},
'concept' => '2'
};
I think $data{line1} {$cell[0]} is better written as $data{line1}{$cell[0]} or (my preference) $data{line1}->{$cell[0]}.
I included the scalar $file and the arrrays #row and #cell to demonstrate what your code means.
$data{file} = $file;
adds the contents of $file to your hash with the key file.
$data{concept} = $#row;
adds the last index of #row to your hash with the key concept. In my example the last index is 2, since the indexes in #row are 0, 1 and 2.
$data{line1} {$cell[0]} = $cell[1];
adds a hash ref to your hash with the key line1 (through autovivification) and adds the element $cell[1] to this hash ref with the key $cell[0]. Autovivification in this case means that Perl associates line1 with a hash ref and creates it, because you're accessing it with {$cell[0]}. That saves you the trouble of having to write:
$data{line} = {};
$data{line}{$cell[0]} = $cell[1];