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associative arrays

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    This subchapter looks at associative arrays.

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    This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.

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associative arrays

    This subchapter looks at associative arrays.

Stanford Perl essentials

    This [the following section until marked as end of Stanford University items] is document #108 [Essential Perl] in the Stanford CS Education Library --see http://cslibrary.stanford.edu/108/. This document is free to be used, reproduced, or sold so long as this paragraph and the copyright are clearly. Copyright 2000-2002, Nick Parlante, nick.parlante@cs.stanford.edu.

5. Hash Arrays -- %

    Hash arrays, also known as “associative” arrays, are a built-in key/value data structure. Hash arrays are optimized to find the value for a key very quickly. Hash array variables begin with a percent sign (%) and use curly braces { } to access the value for a particular key. If there is no such key in the array, the value returned is undef. The keys are case sensitive, so you may want to consistently uppercase or lowercase strings before using them as a key (use lc and uc).

  $dict{"bart"}  = "I didn't do it";
  $dict{"homer"} = "D'Oh";
  $dict{"lisa"}  = "";

  ## %dict now contains the key/value pairs (("bart" => "I didn't do it"),
  ## ("homer" => "D'oh"), ("lisa" => ""))

  $string = $dict{"bart"};    ## Lookup the key "bart" to get
                              ## the value "I didn't do it"

  $string = $dict{"marge"};   ## Returns undef -- there is no entry for "marge"

  $dict{"homer"} = "Mmmm, scalars"; ## change the value for the key
                                    ## "homer" to "Mmmm, scalars"

    A hash array may be converted back and forth to an array where each key is immediately followed by its value. Each key is adjacent to its value, but the order of the key/value pairs depends on the hashing of the keys and so appears random. The “keys” operator returns an array of the keys from an associative array. The “values” operator returns an array of all the values, in an order consistent with the keys operator.

    @array = %dict;

    ## @array will look something like
    ##  ("homer", "D'oh", "lisa", "", "bart", "I didn't do it");
    ##
    ## (keys %dict) looks like ("homer", "lisa, "bart")
    ## or use (sort (keys %dict))

    You can use => instead of comma and so write a hash array value this cute way…

    %dict = (
      "bart" => "I didn't do it",
      "homer" => "D'Oh",
      "lisa" => "",
    );

    In Java or C you might create an object or struct to gather a few items together. In Perl you might just throw those things together in a hash array.

    This [the above section] is document #108 [Essential Perl] in the Stanford CS Education Library --see http://cslibrary.stanford.edu/108/. This document is free to be used, reproduced, or sold so long as this paragraph and the copyright are clearly. Copyright 2000-2002, Nick Parlante, nick.parlante@cs.stanford.edu.

end of Stanford Perl essentials


free music player coding example

    Coding example: I am making heavily documented and explained open source code for a method to play music for free — almost any song, no subscription fees, no download costs, no advertisements, all completely legal. This is done by building a front-end to YouTube (which checks the copyright permissions for you).

    View music player in action: www.musicinpublic.com/.

    Create your own copy from the original source code/ (presented for learning programming).


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    Created: December 18, 2010

    Last Updated: December 18, 2010


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