use strict;
use warnings;
use Data::Dumper;
$Data::Dumper::Sortkeys = 1;

my @lines1 = split /\n/, <<EOF;
car coord bike 0.6
car random cat 0.1
car mero door 0.6
EOF

my @lines2 = split /\n/, <<EOF;
truck random dog 0.3
truck mero door 0.5
EOF

my %data;

for (@lines1, @lines2) {
    my ($k1, $k2, $v) = (split)[1 .. 3];
    my $k = "$k1 $k2";
    if (exists $data{$k}) {
        $data{$k} = $v if $data{$k} > $v;
    }
    else {
        $data{$k} = $v;
    }
}

print Dumper(\%data);

__END__

$VAR1 = {
          'coord bike' => '0.6',
          'mero door' => '0.5',
          'random cat' => '0.1',
          'random dog' => '0.3'
        };