in reply to Re^3: Cartesian Cross-Products
in thread Cartesian Cross-Products

Hi, Perl n00b here. Check out my recursive solution for any number of sets. Feel the scheme. 
sub cartesian {
    my @sets = @_;
    # base case
    if (@sets == 0) {
        return ([]);
    }
    my @first = @{@sets[0]};
    # recursive call
    shift @sets;
    my @rest = cartesian(@sets);
    my @result = ();
    foreach my $element (@first) { 
        foreach my $product (@rest) { 
            my @newSet = @{$product};
            unshift (@newSet, $element);
            push (@result, \@newSet);
        }
    }
    return @result;
}

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Re^5: Cartesian Cross-Products
by psini (Deacon) on Aug 09, 2010 at 17:54 UTC

    Update: Sorry, deleted rerroneous post

    Rule One: "Do not act incautiously when confronting a little bald wrinkly smiling man."

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Re^5: Cartesian Cross-Products
by drt (Initiate) on Feb 15, 2012 at 21:54 UTC

    I had the same thought also (to use a recursive algorithm), but your code didn't seem complete or it didn't work the way I expected. There are certainly more Perlish ways to code this with map etc., but it works. Cartesian product of multiple lists using recursion.

    use Data::Dumper;

my $letters = [qw(a b c)];
my $numbers = [1..3];
my $words   = [qw(you me)];

my $result = cartesian($letters, $numbers, $words);

print Dumper( $result );

sub cartesian {
  my ($set, @sets) = @_;

  my @expanded;

  # base case
  if ( !@sets ) {
    foreach ( @{$set} ){
      push @expanded, [$_];
    }
  }

  # recursive call
  else {
    my @product = @{ cartesian(@sets) };
    foreach my $element ( @{$set} ) {
      foreach my $product ( @product ) {
        push @expanded, [ $element, @{$product} ];
      }
    }
  }

  return \@expanded;
}

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