sub filter {
  my $where = shift;
  my @in = @_;
  
  # This class method is used to filter an array of hashrefs against a set of criteria defined in $where.
  # Example:
  #   @matching_hosts = filter( { site => 56, type => 4 }, @all_hosts);
  # In this example, @matching_hosts will only contain those hashrefs that would return TRUE for the following code:
  #   ($_->{'site'} eq '56' && $_->{'type'} eq '4')
  # Note that the "eq" and "&&" are implied; no other operators are supported.

  # The order of the array is not affected.

  my @out = ();

  foreach my $record (@in) {
    my $keep = 1;
    foreach my $field (keys %{$where}) {
      unless ($record->{$field} eq $where->{$field}) {
        $keep = 0;
        last;
      }
      push @out, $record if $keep;
    }
  }

  return @out;
}

##</code><code>##

sub filter {
  my $where = shift;
  my @in = @_;
  
  # This class method is used to filter an array of hashrefs against a set of criteria defined in $where.
  # Example:
  #   @matching_hosts = filter( { site => 56, type => 4 }, @all_hosts);
  # In this example, @matching_hosts will only contain those hashrefs that would return TRUE for the following code:
  #   ($_->{'site'} eq '56' && $_->{'type'} eq '4')
  # Note that the "eq" and "&&" are implied; no other operators are supported.

  # The order of the array is not affected.

  my @out = ();

  # Make one pass per match term
  foreach my $field (keys %{$where}) {
    my $value = $where->{$field};
      @out = grep { $_->{$field} eq $value } @in;
    @in = @out; # Prepare for next pass (if any)
  }

  return @out;
}

##</code><code>##

$ cat foreach_inner
#!/usr/bin/perl

use strict;
use warnings;

foreach my $foo (1 .. 3) {
  foreach my $bar (1 .. 10000000) {
    my $pointless = "$foo.$bar";
  }
}

##</code><code>##

$ time ./foreach_inner

real	0m8.975s
user	0m8.954s
sys	0m0.013s

##</code><code>##

$ cat foreach_outer
#!/usr/bin/perl

use strict;
use warnings;

foreach my $foo (1 .. 10000000) {
  foreach my $bar (1 .. 3) {
    my $pointless = "$foo.$bar";
  }
}

##</code><code>##

$ time ./foreach_outer

real	0m14.106s
user	0m14.092s
sys	0m0.003s