looping over multiple arrays

Just an example of building an iterator with a closure to walk through multiple arrays in parallel (maybe you have a table (2d array) and want to walk the columns). This is just a simple one that runs through the arrays and then resets so it can be used again:

sub parallel_it {
    my @arr_refs = @_;
    my $iter = 0;
    return sub {
        my @return = map{$_->[$iter]}@arr_refs;
        $iter++;
        return @return if grep{defined $_}@return;
        $iter = 0;
        return;
    };
};
my @one   = (0, 1, 2, 3, 4, 5, 6);
my @two   = qw/Sun Mon Tue Wed Thu Fri Sat/;
my @three = qw/Zeroday Oneday Twoday Threeday 
               Fourday Fiveday Sixday/;

my $triples = parallel_it( \(@one,@two,@three) );
while( my($a, $b, $c) = $triples->() ){
    print "$a:$b:$c\n";
}

# update @one and go again
@one = qw/A B C D E F G/;
while( my($a, $b, $c) = $triples->() ){
    print "$a:$b:$c\n";
}

my @table = ( [ 1, undef, 3, 4],
              [ 6, 7,],
              [qw/a b c d e f/],
             );
my $columns = parallel_it(@table);
while( my @col = $columns->() ){
    print join(',', map{ $_ ? $_ : ' ' } @col),"\n";
}
[download]

Back to Cool Uses for Perl