Separating CSV file into key and array - arrays

Question

I am new to perl, and I am trying to separate a csv file (has 10 comma-separated items per line) into a key (first item) and an array (9 items) to put in a hash. Eventually, I want to use an if function to match another variable to the key in the hash and print out the elements in the array.
Here's the code I have, which doesn't work right.
use strict;
use warnings;
my %hash;
my $in2 = "metadata1.csv";
open IN2, "<$in2" or die "Cannot open the file: $!";
while (my $line = <IN2>) {
my ($key, #value) = split (/,/, $line, 2);
%hash = (
$key => #value
);
}
foreach my $key (keys %hash)
{
print "The key is $key and the array is $hash{$key}\n";
}
Thank you for any help!

Answer 1

Don't use 2 as the third argument to split: it will split the line to only two elements, so there'll be just one #value.
Also, by doing %hash =, you're overwriting the hash in each iteration of the loop. Just add a new key/value pair:
$hash{$key} = \#value;
Note the \ sign: you can't store an array directly as a hash value, you have to store a reference to it. When printing the value, you have to dereference it back:
#! /usr/bin/perl
use warnings;
use strict;
my %hash;
while (<DATA>) {
my ($key, #values) = split /,/;
$hash{$key} = \#values;
}
for my $key (keys %hash) {
print "$key => #{ $hash{$key} }";
}
__DATA__
id0,1,2,a
id1,3,4,b
id2,5,6,c
If your CSV file contains quoted or escaped commas, you should use Text::CSV.

Answer 2

First of all hash can have only one unique key, so when you have lines like these in your CSV file:
key1,val11,val12,val13,val14,val15,val16,val17,val18,val19
key1,val21,val22,val23,val24,val25,val26,val27,val28,val29
after adding both key/value pairs with 'key1' key to the hash, you'll get just one pair saved in the hash, the one that were added to the hash later.
So to keep all records, the result you probably need array of hashes structure, where value of each hash is an array reference, like this:
#result = (
{ 'key1' => ['val11','val12','val13','val14','val15','val16','val17','val18','val19'] },
{ 'key1' => ['val21','val22','val23','val24','val25','val26','val27','val28','val29'] },
{ 'and' => ['so on'] },
);
In order to achieve that your code should become like this:
use strict;
use warnings;
my #AoH; # array of hashes containing data from CSV
my $in2 = "metadata1.csv";
open IN2, "<$in2" or die "Cannot open the file: $!";
while (my $line = <IN2>) {
my #string_bits = split (/,/, $line);
my $key = $string_bits[0]; # first element - key
my $value = [ #string_bits[1 .. $#string_bits] ]; # rest get into arr ref
push #AoH, {$key => $value}; # array of hashes structure
}
foreach my $hash_ref (#AoH)
{
my $key = (keys %$hash_ref)[0]; # get hash key
my $value = join ', ', #{ $hash_ref->{$key} }; # join array into str
print "The key is '$key' and the array is '$value'\n";
}