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PERL

Perl Lists: Utilizing List::Util
By: James Payne
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    2008-04-14


    Table of Contents:
  • Perl Lists: Utilizing List::Util
  • First Up On the Block
  • Making First a Little More Complicated
  • Max()ing It Out
  • My String is Bigger Than Yours: The MaxStr(List) Story

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    Perl Lists: Utilizing List::Util - First Up On the Block
    ( Page 2 of 5 )

    The first{block}list subroutine, as stated above, returns the first value in a list. If you have a list that contains the following data, in this order: Hercules, Perseus, Theseus, and Mister T (basically a list of Greek heroes) and you use the first{block}list subroutine on it, then your result would be: Hercules. This is because he is the first piece of data in the list. Don't believe it? Let's go to the code:


    #!/usr/bin/perl

    use List::Util qw(first);

    @Greek=('Hercules','Perseus','Theseus','Mister T');

    $Front = first {$_} @Greek;

    print $Front;

    The result?

      Hercules

    We can do the same with numbers:


    #!/usr/bin/perl

    use List::Util qw(first);

    @Nums=(1,2,3,4);

    $Front = first {$_} @Nums;

    print $Front;

    Which results in:

      1

    But what if we don't want just the first value in a list? What if we want to set certain criteria that must be met? We can do so by adding conditionals to our subroutine:


    #!/usr/bin/perl

    use List::Util qw(first);

    @Nums=(1,2,3,4);

    $Front = first {$_>2} @Nums;

    print $Front;

    In the above code, we modify the parameter by adding a greater than two conditional. Simply put, we want the first value larger than the number 2. The result, of course, is:

      3

    And likewise, we can also use things like AND and OR as well:


    #!/usr/bin/perl

    use List::Util qw(first);

    @Nums=(1,2,3,4);

    $Front = first {$_<5 && $_>3} @Nums;

    print $Front;

    Here, we use the following criteria: less than five, yet greater than three. This returns the number four.



     
     
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