Perl Hashes of Arrays and Some issues - arrays

Question

I currently have a csv file that looks like this:
a,b
a,d
a,f
c,h
c,d
So I saved these into a hash such that the key "a" is an array with "b,d,f" and the key "c" is an array with "h,d"... this is what I used for that:
while(<$fh>)
{
chomp;
my #row = split /,/;
my $cat = shift #row;
$category = $cat if (!($cat eq $category)) ;
push #{$hash{$category}}, #row;
}
close($fh);
Not sure about the efficiency but it seems to work when I do a Data Dump...
Now, the issue I'm having is this; I want to create a new file for each key, and in each of those files I want to print every element in the key, as such:
file "a" would look like this:
b
d
f
<end of file>
Any ideas? Everything I've tried isn't working, I'm not too familiar / experienced with hashes...
Thanks in advance :)

Answer 1

The output process is very simple using the each iterator, which provides the key and value pair for the next hash element in a single call
use strict;
use warnings;
use autodie;
open my $fh, '<', 'myfile.csv';
my %data;
while (<$fh>) {
chomp;
my ($cat, $val) = split /,/;
push #{ $data{$cat} }, $val;
}
while (my ($cat, $values) = each %data) {
open my $out_fh, '>', $cat;
print $out_fh "$_\n" for #$values;
}

Answer 2

#!/usr/bin/perl
use strict;
use warnings;
my %foos_by_cat;
{
open(my $fh_in, '<', ...) or die $!;
while (<$fh_in>) {
chomp;
my ($cat, $foo) = split /,/;
push #{ $foos_by_cat{$cat} }, $foo;
}
}
for my $cat (keys %foos_by_cat) {
open(my $fh_out, '>', $cat) or die $!;
for my $foo (#{ $foos_by_cat{$cat} }) {
print($fh_out "$foo\n");
}
}
I wrote the inner loop as I did to show the symmetry between reading and writing, but it can also be written as follows:
print($fh_out "$_\n") for #{ $foos_by_cat{$cat} };