#!perl

use strict;
use warnings;
use Text::CSV qw( csv );

my $magic_column = 3;    #0-indexed

my $aoa = csv( in => $ARGV[0] );

my %uniq = ();
my $head = shift @$aoa;
foreach my $line (@$aoa) {
    my $key    = join( ',', @{$line}[ 0 .. $magic_column - 1 ] );
    my $suffix = join( ',', @{$line}[ $magic_column + 1 .. $#$line ] );
    $uniq{$key} //= [ [], $suffix ];
    push @{ $uniq{$key}[0] }, $line->[$magic_column];
}

print join( ',', @$head ), "\n";
foreach my $line ( sort { lc $a cmp lc $b } keys %uniq ) {
    my $magic = join( ',', sort { lc $a cmp lc $b } @{ $uniq{$line}[0] } );
    if ( @{ $uniq{$line}[0] } > 1 ) { $magic = '"' . $magic . '"'; }
    print $line, ',', $magic, ',', $uniq{$line}[1], "\n";
}