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From: Tom Christiansen <[email protected]>
Newsgroups: comp.lang.perl.misc,comp.lang.perl.announce
Subject: PDSC Recipes for Hashes of Lists (part 2 of 5)
Followup-To: comp.lang.perl.misc
Date: 2 Oct 1995 01:51:59 GMT
Organization: Perl Consulting and Training
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           PDSC: The Perl Data Structures Cookbook
                   part 2 of 5: Hashes of Lists

                   by Tom Christiansen
                   <[email protected]>

                   release 0.1 (untested, may have typos)
                   Sunday, 1 October 1995

Declaration of a HASH OF LISTS:

   %HoL = (
          "flintstones"        => [ "fred", "barney" ],
          "jetsons"            => [ "george", "jane", "elroy" ],
          "simpsons"           => [ "homer", "marge", "bart" ],
        );

Generation:

   # reading from file
   # flintstones: fred barney wilma dino
   while ( <> ) {
       next unless s/^(.*?):\s*//;
       $HoL{$1} = [ split ];
   }

   # reading from file; more temps
   # flintstones: fred barney wilma dino
   while ( $line = <> ) {
       ($who, $rest) = split /:\s*/, $line, 2;
       @fields = split ' ', $rest;
       $HoL{$who} = [ @fields ];
   }

   # calling a function that returns a list
   for $group ( "simpsons", "jetsons", "flintstones" ) {
       $HoL{$group} = [ get_family($group) ];
   }

   # likewise, but using temps
   for $group ( "simpsons", "jetsons", "flintstones" ) {
       @members = get_family($group);
       $HoL{$group} = [ @members ];
   }

   # append new members to an existing family
   push @{ $HoL{"flintstones"} }, "wilma", "betty";


Access and Printing:

   # one element
   $HoL{flintstones}[0] = "Fred";

   # another element
   $HoL{simpsons}[1] =~ s/(\w)/\u$1/;

   # print the whole thing
   foreach $family ( keys %HoL ) {
       print "$family: @{ $HoL{$family} }\n"
   }

   # print the whole thing with indices
   foreach $family ( keys %HoL ) {
       print "family: ";
       foreach $i ( 0 .. $#{ $HoL{$family} ) {
           print " $i = $HoL{$family}[$i]";
       }
       print "\n";
   }

   # print the whole thing sorted by number of members
   foreach $family ( sort { @{$HoL{$b}} <=> @{$HoL{$b}} } keys %HoL ) {
       print "$family: @{ $HoL{$family} }\n"
   }
   # print the whole thing sorted by number of members and name
   foreach $family ( sort { @{$HoL{$b}} <=> @{$HoL{$a}} } keys %HoL ) {
       print "$family: ", join(", ", sort @{ $HoL{$family}), "\n";
   }