my %monks_by_level;

for my $monk ( @array_of_monks )
{
  my $level = $monk->level(); # or ->{level} or whatever...
  push @{ $monks_by_level{$level} }, $monk;
}

for my $level ( keys %monks_by_level )
{
  print "doing $level...\";
  callToPrayer( $monks_by_level{$level} );
}

sub callToPrayer
{
  my ($monks) = @_;

  for my $monk ( @$monks )
  {
    print "$monk->name() here!\n";
  }
}