use strict;
use warnings;
use Data::Dumper;

my $data1=[
{key=>'a1',value=>'vala1'},
{key=>'a2',value=>'vala2'},
{key=>'a3',value=>'vala3'},
{key=>'b1',value=>'valb1'},
{key=>'b2',value=>'valb2'},
{key=>'c2',value=>'valc2'},
];

my %ret;
#one map
%ret = map{ $_->{key} => $_->{value} if($_->{key} =~/^a\d+/) } @$data1;
print "map ver\n";
print Dumper \%ret;

#grep and map
%ret = map{ $_->{key} => $_->{value} } grep{ $_->{key} =~ /^a\d+/ } @$data1; 
print "grep,map ver\n";
print Dumper \%ret;

#foreach
%ret=();
foreach my $r (@$data1){
	$ret{$r->{key}} = $r->{value} if ( $r->{key} =~ /^a\d+/ );
}
print "foreach ver\n";
print Dumper \%ret;


##</code><code>##

Odd number of elements in hash assignment at test.pl line 15.
map ver
$VAR1 = {
          '' => undef,   <====THIS ONE
          'a2' => 'vala2',
          'a1' => 'vala1',
          'a3' => 'vala3'
        };
grep,map ver
$VAR1 = {
          'a2' => 'vala2',
          'a1' => 'vala1',
          'a3' => 'vala3'
        };
foreach ver
$VAR1 = {
          'a2' => 'vala2',
          'a1' => 'vala1',
          'a3' => 'vala3'
        };