#!/usr/bin/perl
use strict;
use warnings;

my %results;
open my $fh, '<', 'file1.csv' or die $!;

while ( <$fh> ) {
    chomp ;
    my ($a1, $b1, $actDt, $inactDt) = split /,/;
    
    if (exists $results{$a1,$b1} ) {
    
        if ($actDt < $results{$a1,$b1}{ACTDATE}) {
            $results{$a1,$b1}{ACTDATE} = $actDt;
        }
            
        if (!$inactDt || !$results{$a1,$b1}{INACTDATE}) {
            $results{$a1,$b1}{INACTDATE} = '' ;
        }
        elsif($inactDt > $results{$a1,$b1}{INACTDATE} ) {
            $results{$a1,$b1}{INACTDATE} = $inactDt;
        }
    }
    else {  
        # Create new entry in hash
        $results{$a1,$b1} = {
            A1 => $a1,
            B1 => $b1,
            ACTDATE => $actDt,
            INACTDATE => $inactDt,
        };
    }
}
    
foreach ( sort keys %results ) {
    my $a1 = $results{ $_ }{A1} ;
    my $b1 = $results{ $_ }{B1} ;
    my $actDt = $results{ $_ }{ACTDATE};
    my $inactDt = $results{ $_ }{INACTDATE};
    print "$a1,$b1,$actDt,$inactDt\n" ;
}