#!/usr/bin/perl
use strict;

my %r;
$r{123}{a}=3;
$r{123}{b}=2;
$r{456}{c}=5;
$r{456}{d}=7;

map { print "\$r{$_->[0]}{$_->[1]} ==> $r{$_->[0]}{$_->[1]}\n" }
map { [$_,(sort { $r{$_}->{$b} <=> $r{$_}->{$a} } keys %{$r{$_}})[0]]}
  keys %r;

##</code><code>##

$r{456}{d} ==> 7
$r{123}{a} ==> 3

##</code><code>##

my %rmax;
$rmax{$_} = (sort { $r{$_}->{$b} <=> $r{$_}->{$a} } keys %{$r{$_}})[0]
  for keys %r;
print "\$r{$_}{$rmax{$_}} ==> $r{$_}{$rmax{$_}}\n" for keys %rmax;

##</code><code>##

$r{123}{a} ==> 3
$r{456}{d} ==> 7