use strict ;
use warnings ;
my %results = () ;
while ( <DATA> ) {
	chomp ;
	my @row = split /,/, $_ ;
	if ( exists $results{ $row[0] } ) {
		# Update existing hash entries
		if ( ( $row[2] ) <
			 $results{ $row[0] }->{ 'MIN ACTDATE' }
		) {
			$results{ $row[0] }->{ 'B1 MIN ACTDATE' } = $row[1] ;
			$results{ $row[0] }->{ 'MIN ACTDATE' } = $row[2] ;
		}
		if ( !( defined $row[3] &&
				defined $results{ $row[0] }->{ 'MAX DEACTDATE' } )
		) {
			$results{ $row[0] }->{ 'B1 MAX ACTDATE' } = undef ;
			$results{ $row[0] }->{ 'MAX DEACTDATE' } = undef ;
		} elsif ( ( $row[3] ) >
				  ( $results{ $row[0] }->{ 'MAX DEACTDATE' } )
		) {
			$results{ $row[0] }->{ 'B1 MAX ACTDATE' } = $row[1] ;
			$results{ $row[0] }->{ 'MAX DEACTDATE' } = $row[3] ;
		}
	} else {
		# Create new entry in hash
		$results{ $row[0] } = {
			'A1' => $row[0],
			'B1 MIN ACTDATE' => $row[1],
			'B1 MAX ACTDATE' => $row[1],
			'MIN ACTDATE' => $row[2],
			'MAX DEACTDATE' => $row[3],
		}
	}
}
foreach ( sort keys %results ) {
	my $a1 = $results{ $_ }->{ 'A1' } ;
	my $b1ma = $results{ $_ }->{ 'B1 MIN ACTDATE' } ;
	my $b1md = $results{ $_ }->{ 'B1 MAX ACTDATE' } // 'NULL' ;
	my $mad = $results{ $_ }->{ 'MIN ACTDATE' } ;
	my $mdad = $results{ $_ }->{ 'MAX DEACTDATE' } // 'NULL' ;
	print "$a1,$b1ma:$b1md,$mad,$mdad\n" ;
}
__DATA__
7900724666,200906888,20180416,20180522
7900724666,200906888,20180601,20180720
7900724666,200906888,20180406,20180411
7900724677,200906872,20180301,20180330
7900724677,200906871,20180101,20180228
7900724677,200906873,20180401,20180420
7900724688,200906881,20180101,20180228
7900724688,200906881,20180303,20180330
7900724688,200906882,20180404,20180430
7900724688,200906883,20180508,20180620
7900724699,200906891,20180101,20180228
7900724699,200906891,20180303,20180330
7900724699,200906892,20180404,20180430
7900724699,200906893,20180508,

##</code><code>##

7900724666,200906888:200906888,20180406,20180720
7900724677,200906871:200906873,20180101,20180420
7900724688,200906881:200906883,20180101,20180620
7900724699,200906891:NULL,20180101,NULL