Programming Perl, 4th Edition

Generation of a Hash of Arrays

Here are some techniques for populating a hash of arrays. To read from a file with the following format:

flintstones: fred barney wilma dino
jetsons:     george jane elroy
simpsons:    homer marge bart

you could use either of the following two loops:

while ( <> ) {
     next unless s/^(.*?):\s*//;
     $HoA{$1} = [ split ];
 }

 while ( $line = <> ) {
     ($who, $rest) = split /:\s*/, $line, 2;
     @fields = split " ", $rest;
     $HoA{$who} = [ @fields ];
 }

If you have a subroutine get_family that returns an array, you can use it to stuff %HoA with either of these two loops:

for $group ( "simpsons", "jetsons", "flintstones" ) {
    $HoA{$group} = [ get_family($group) ];
}

for $group ( "simpsons", "jetsons", "flintstones" ) {
    @members = get_family($group);
    $HoA{$group} = [ @members ];
}

You can append new members to an existing array like so:

push @{ $HoA{flintstones} }, "wilma", "pebbles";