my $array = [[apple, a1], [apple, a2], [apple, a3]]; 
my %hash = ();
foreach (@{$array}) {
    $hash{$_->[0]} = [] unless defined($hash{$_->[0]});
    push (@{$hash{$_->[0]}}, $_->[1]); 
}

##</code><code>##

use List::Util qw(reduce);

my $array = [[apple, a1], [apple, a2], [apple, a3]]; 
my $result = [];
unshift(@$array, []);
push @$result, reduce { 
	push(@$a, $b->[0]) unless exists $a->[0];
	push(@$a, $b->[1]); 
	$a;
} @$array;