Recipes for PDSC #4: Hashes of Hashes

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",	},     );

Generation of a HASH OF HASHES:

# reading from file# flintstones: lead=fred pal=barney wife=wilma pet=dinowhile ( <> ) {    next unless s/^(.*?):\s*//;    $who = $1;    for $field ( split ) {	($key, $value) = split /=/, $field;	$HoH{$who}{$key} = $value;    }}# reading from file; more tempswhile ( <> ) {    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 hashfor $group ( "simpsons", "jetsons", "flintstones" ) {    $HoH{$group} = { get_family($group) };}# likewise, but using tempsfor $group ( "simpsons", "jetsons", "flintstones" ) {    %members = get_family($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};}

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