perldsc.pod

ARM上的如果你对底层感兴趣

     $HoL{$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";

=head2 Access and Printing of a HASH OF LISTS

 # 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{$a}} } keys %HoL ) {
     print "$family: @{ $HoL{$family} }\n"
 }

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

=head1 LISTS OF HASHES

=head2 Declaration of a LIST OF HASHES

 @LoH = (
        {
            Lead     => "fred",
            Friend   => "barney",
        },
        {
            Lead     => "george",
            Wife     => "jane",
            Son      => "elroy",
        },
        {
            Lead     => "homer",
            Wife     => "marge",
            Son      => "bart",
        }
  );

=head2 Generation of a LIST OF HASHES

 # reading from file
 # format: LEAD=fred FRIEND=barney
 while ( <> ) {
     $rec = {};
     for $field ( split ) {
         ($key, $value) = split /=/, $field;
         $rec->{$key} = $value;
     }
     push @LoH, $rec;
 }


 # reading from file
 # format: LEAD=fred FRIEND=barney
 # no temp
 while ( <> ) {
     push @LoH, { split /[\s+=]/ };
 }

 # calling a function  that returns a key,value list, like
 # "lead","fred","daughter","pebbles"
 while ( %fields = getnextpairset() ) {
     push @LoH, { %fields };
 }

 # likewise, but using no temp vars
 while (<>) {
     push @LoH, { parsepairs($_) };
 }

 # add key/value to an element
 $LoH[0]{pet} = "dino";
 $LoH[2]{pet} = "santa's little helper";

=head2 Access and Printing of a LIST OF HASHES

 # one element
 $LoH[0]{lead} = "fred";

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

 # print the whole thing with refs
 for $href ( @LoH ) {
     print "{ ";
     for $role ( keys %$href ) {
         print "$role=$href->{$role} ";
     }
     print "}\n";
 }

 # print the whole thing with indices
 for $i ( 0 .. $#LoH ) {
     print "$i is { ";
     for $role ( keys %{ $LoH[$i] } ) {
         print "$role=$LoH[$i]{$role} ";
     }
     print "}\n";
 }

 # print the whole thing one at a time
 for $i ( 0 .. $#LoH ) {
     for $role ( keys %{ $LoH[$i] } ) {
         print "elt $i $role is $LoH[$i]{$role}\n";
     }
 }

=head1 HASHES OF HASHES

=head2 Declaration of a HASH OF HASHES

 %HoH = (
        flintstones => {
		lead      => "fred",
		pal       => "barney",
        },
        jetsons     => {
		lead      => "george",
		wife      => "jane",
		"his boy" => "elroy",
        },
        simpsons    => {
		lead      => "homer",
		wife      => "marge",
		kid       => "bart",
	},
 );

=head2 Generation of a HASH OF HASHES

 # reading from file
 # flintstones: lead=fred pal=barney wife=wilma pet=dino
 while ( <> ) {
     next unless s/^(.*?):\s*//;
     $who = $1;
     for $field ( split ) {
         ($key, $value) = split /=/, $field;
         $HoH{$who}{$key} = $value;
     }


 # reading from file; more temps
 while ( <> ) {
     next unless s/^(.*?):\s*//;
     $who = $1;
     $rec = {};
     $HoH{$who} = $rec;
     for $field ( split ) {
         ($key, $value) = split /=/, $field;
         $rec->{$key} = $value;
     }
 }

 # calling a function  that returns a key,value hash
 for $group ( "simpsons", "jetsons", "flintstones" ) {
     $HoH{$group} = { get_family($group) };
 }

 # likewise, but using temps
 for $group ( "simpsons", "jetsons", "flintstones" ) {
     %members = get_family($group);
     $HoH{$group} = { %members };
 }

 # append new members to an existing family
 %new_folks = (
     wife => "wilma",
     pet  => "dino",
 );

 for $what (keys %new_folks) {
     $HoH{flintstones}{$what} = $new_folks{$what};
 }

=head2 Access and Printing of a HASH OF HASHES

 # one element
 $HoH{flintstones}{wife} = "wilma";

 # another element
 $HoH{simpsons}{lead} =~ s/(\w)/\u$1/;

 # print the whole thing
 foreach $family ( keys %HoH ) {
     print "$family: { ";
     for $role ( keys %{ $HoH{$family} } ) {
         print "$role=$HoH{$family}{$role} ";
     }
     print "}\n";
 }

 # print the whole thing  somewhat sorted
 foreach $family ( sort keys %HoH ) {
     print "$family: { ";
     for $role ( sort keys %{ $HoH{$family} } ) {
         print "$role=$HoH{$family}{$role} ";
     }
     print "}\n";
 }


 # print the whole thing sorted by number of members
 foreach $family ( sort { keys %{$HoH{$b}} <=> keys %{$HoH{$a}} } keys %HoH ) {
     print "$family: { ";
     for $role ( sort keys %{ $HoH{$family} } ) {
         print "$role=$HoH{$family}{$role} ";
     }
     print "}\n";
 }

 # establish a sort order (rank) for each role
 $i = 0;
 for ( qw(lead wife son daughter pal pet) ) { $rank{$_} = ++$i }

 # now print the whole thing sorted by number of members
 foreach $family ( sort { keys %{ $HoH{$b} } <=> keys %{ $HoH{$a} } } keys %HoH ) {
     print "$family: { ";
     # and print these according to rank order
     for $role ( sort { $rank{$a} <=> $rank{$b} }  keys %{ $HoH{$family} } ) {
         print "$role=$HoH{$family}{$role} ";
     }
     print "}\n";
 }


=head1 MORE ELABORATE RECORDS

=head2 Declaration of MORE ELABORATE RECORDS

Here's a sample showing how to create and use a record whose fields are of
many different sorts:

     $rec = {
	 TEXT      => $string,
	 SEQUENCE  => [ @old_values ],
	 LOOKUP    => { %some_table },
	 THATCODE  => \&some_function,
	 THISCODE  => sub { $_[0] ** $_[1] },
	 HANDLE    => \*STDOUT,
     };

     print $rec->{TEXT};

     print $rec->{LIST}[0];
     $last = pop @ { $rec->{SEQUENCE} };

     print $rec->{LOOKUP}{"key"};
     ($first_k, $first_v) = each %{ $rec->{LOOKUP} };

     $answer = $rec->{THATCODE}->($arg);
     $answer = $rec->{THISCODE}->($arg1, $arg2);

     # careful of extra block braces on fh ref
     print { $rec->{HANDLE} } "a string\n";

     use FileHandle;
     $rec->{HANDLE}->autoflush(1);
     $rec->{HANDLE}->print(" a string\n");

=head2 Declaration of a HASH OF COMPLEX RECORDS

     %TV = (
        flintstones => {
            series   => "flintstones",
            nights   => [ qw(monday thursday friday) ],
            members  => [
                { name => "fred",    role => "lead", age  => 36, },
                { name => "wilma",   role => "wife", age  => 31, },
                { name => "pebbles", role => "kid",  age  =>  4, },
            ],
        },

        jetsons     => {
            series   => "jetsons",
            nights   => [ qw(wednesday saturday) ],
            members  => [
                { name => "george",  role => "lead", age  => 41, },
                { name => "jane",    role => "wife", age  => 39, },
                { name => "elroy",   role => "kid",  age  =>  9, },
            ],
         },

        simpsons    => {
            series   => "simpsons",
            nights   => [ qw(monday) ],
            members  => [
                { name => "homer", role => "lead", age  => 34, },
                { name => "marge", role => "wife", age => 37, },
                { name => "bart",  role => "kid",  age  =>  11, },
            ],
         },
      );

=head2 Generation of a HASH OF COMPLEX RECORDS

     # reading from file
     # this is most easily done by having the file itself be
     # in the raw data format as shown above.  perl is happy
     # to parse complex data structures if declared as data, so
     # sometimes it's easiest to do that

     # here's a piece by piece build up
     $rec = {};
     $rec->{series} = "flintstones";
     $rec->{nights} = [ find_days() ];

     @members = ();
     # assume this file in field=value syntax
     while (<>) {
         %fields = split /[\s=]+/;
         push @members, { %fields };
     }
     $rec->{members} = [ @members ];

     # now remember the whole thing
     $TV{ $rec->{series} } = $rec;

     ###########################################################
     # now, you might want to make interesting extra fields that
     # include pointers back into the same data structure so if
     # change one piece, it changes everywhere, like for examples
     # if you wanted a {kids} field that was an array reference
     # to a list of the kids' records without having duplicate
     # records and thus update problems.
     ###########################################################
     foreach $family (keys %TV) {
         $rec = $TV{$family}; # temp pointer
         @kids = ();
         for $person ( @{ $rec->{members} } ) {
             if ($person->{role} =~ /kid|son|daughter/) {
                 push @kids, $person;
             }
         }
         # REMEMBER: $rec and $TV{$family} point to same data!!
         $rec->{kids} = [ @kids ];
     }

     # you copied the list, but the list itself contains pointers
     # to uncopied objects. this means that if you make bart get
     # older via

     $TV{simpsons}{kids}[0]{age}++;

     # then this would also change in
     print $TV{simpsons}{members}[2]{age};

     # because $TV{simpsons}{kids}[0] and $TV{simpsons}{members}[2]
     # both point to the same underlying anonymous hash table

     # print the whole thing
     foreach $family ( keys %TV ) {
         print "the $family";
         print " is on during @{ $TV{$family}{nights} }\n";
         print "its members are:\n";
         for $who ( @{ $TV{$family}{members} } ) {
             print " $who->{name} ($who->{role}), age $who->{age}\n";
         }
         print "it turns out that $TV{$family}{lead} has ";
         print scalar ( @{ $TV{$family}{kids} } ), " kids named ";
         print join (", ", map { $_->{name} } @{ $TV{$family}{kids} } );
         print "\n";
     }

=head1 Database Ties

You cannot easily tie a multilevel data structure (such as a hash of
hashes) to a dbm file.  The first problem is that all but GDBM and
Berkeley DB have size limitations, but beyond that, you also have problems
with how references are to be represented on disk.  One experimental
module that does partially attempt to address this need is the MLDBM
module.  Check your nearest CPAN site as described in L<perlmodlib> for
source code to MLDBM.

=head1 SEE ALSO

perlref(1), perllol(1), perldata(1), perlobj(1)

=head1 AUTHOR

Tom Christiansen <F<[e-mail]>>

Last update:
Wed Oct 23 04:57:50 MET DST 1996