#!/usr/local/bin/perl -w
use strict;
use Data::Dumper;

my $row = { title => 'Part1' };

my $parts = [ 'Part1', 'Part2','Part3' ];

my $newLoop = [ grep { $_->{SELECTED}++
                  if $_->{PARTNAME} eq $row->{title}; $_ }
                map +{ 'PARTNAME' => $_ }, @$parts ] ;

warn Dumper($newLoop);
__END__
$VAR1 = [
          {
            'SELECTED' => 1,
            'PARTNAME' => 'Part1'
          },
          {
            'PARTNAME' => 'Part2'
          },
          {
            'PARTNAME' => 'Part3'
          }
        ];


##</code><code>##

#!/usr/local/bin/perl -w
use strict;
use Data::Dumper;

my $row = { title => 'Part1' };

my $parts = [ 'Part1', 'Part2','Part3' ];

my $newLoop = [ map
    +{  
        'PARTNAME' => $_,
        $row->{title} eq $_ ? ('SELECTED' => 1) : (),
    }, @$parts ] ;

warn Dumper($newLoop);