Dynamically Change the Key Value based on Delimiter in Perl - perl

Question

I'm reading from a CSV file and populating a Hash based on Key-Value Pairs.
The First Column of the record is the key, and the rest of the record is the value. However, for some file I need to make first 2 columns as Key and the rest of the record is value. I have written it as below based on if loop by checking the number of Key Columns, but I wanted to know if there is any better way to do this?
use strict;
use warnings;
open my $fh, '<:encoding(utf8)', 'Sample.csv'
or die "Couldn't open Sample.csv";
my %hash;
my $KeyCols=2;
while (<$fh>) {
chomp;
if ($KeyCols==1) {
next unless /^(.*?),(.*)$/;
$hash{$1} = $2;
}
elsif ($KeyCols==2) {
next unless /^(.*?),(.*?),(.*)$/;
$hash{$1.$2} = $3;
}
}

Answer 1

Here is one way to allow for any number of key columns (not just 1 or 2), but it uses split instead of a regex:
use warnings;
use strict;
my %hash;
my $KeyCols = 2;
while (<DATA>) {
chomp;
my #cols = split /,/, $_, $KeyCols+1;
next unless #cols > $KeyCols;
my $v = pop #cols;
my $k = join '', #cols;
$hash{$k} = $v;
}
__DATA__
a,b,c,d,e,f
q,w,e,r,t,y
This is a self-contained code example.
A big assumption is that your CSV file does not contain commas in the data itself. You should be using a CSV parser such as Text::CSV anyway.

Answer 2

Perhaps it is better to define variables at first lines of the code -- otherwise you have to jump all over the code.
You can define regex based on your $KeyCols and processing code will be same as before.
use strict;
use warnings;
use feature 'say';
my $KeyCols = 2;
my $fname = 'Sample.csv';
my %hash;
my $re;
if( $KeyCols == 2 ) {
$re = qr/^(.*?,.*?),(.*)$/
} else {
$re = qr/^(.*?),(.*)$/;
}
open my $fh, '<:encoding(utf8)', $fname
or die "Couldn't open $fname";
while (<$fh>) {
chomp;
next unless /$re/;
$hash{$1} = $2;
}
close $fh;