FAQ 4.47 How do I handle circular lists?

Discussion in 'Perl Misc' started by PerlFAQ Server, Apr 6, 2011.

  1. This is an excerpt from the latest version perlfaq4.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
    to review and update the answers. The latest version of the complete
    perlfaq is at http://faq.perl.org .

    --------------------------------------------------------------------

    4.47: How do I handle circular lists?

    (contributed by brian d foy)

    If you want to cycle through an array endlessly, you can increment the
    index modulo the number of elements in the array:

    my @array = qw( a b c );
    my $i = 0;

    while( 1 ) {
    print $array[ $i++ % @array ], "\n";
    last if $i > 20;
    }

    You can also use "Tie::Cycle" to use a scalar that always has the next
    element of the circular array:

    use Tie::Cycle;

    tie my $cycle, 'Tie::Cycle', [ qw( FFFFFF 000000 FFFF00 ) ];

    print $cycle; # FFFFFF
    print $cycle; # 000000
    print $cycle; # FFFF00

    The "Array::Iterator::Circular" creates an iterator object for circular
    arrays:

    use Array::Iterator::Circular;

    my $color_iterator = Array::Iterator::Circular->new(
    qw(red green blue orange)
    );

    foreach ( 1 .. 20 ) {
    print $color_iterator->next, "\n";
    }



    --------------------------------------------------------------------

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    corrections. The perlfaq-workers also don't have access to every
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    corrections to examples that do not work on particular platforms.
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    PerlFAQ Server, Apr 6, 2011
    #1
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