How to represent nested data structures using Perl 6 classes? - raku

Question

Last time I had to deal with such data, I used something like array-of-hashes, where each hash could have hash values etc. While looping through different indices/keys, it was very difficult not to get lost, so I presume there should be a better solution. Since I have no experience in OOP, I don't know, how to start...
Suppose in our city, we have a Library (whose contents has been digitized into txt-files) with several rooms: 1_red_room, 2_blue_room, and 3_white_room. In every room, there are many books, every book having: author's_name, title, and text (read from txt files) divided into pages(with numbers).
Given a $word, for every room, the program should list:
room_name, with the overall number of `$word` contexts in all its books
list of authors, who use this word, with number of contexts
for every author, list of books, with number of contexts
for every book, list of pages, with number of contexts
Example of the output:
Word: cucumber
TOTAL: 654
1_red_room: 234
author: John Smith: 70
title: "In the wild": 3
page_50: 1
page_150: 2
title: "Hello world": 10
page_1: 2
page_5: 1
page_7: 3
...
...
2_blue_room: 114
author: Wendy Brown
title: "In the dark": 43
page_8: 7
...
So, is there a way to deal with such data with the help of user-defined classes (or probably using some other instruments)?

Answer 1

Here is how I would start at this. I would create a Book class. Then I would create a hash of books %books for each room:
my $total-count = 0;
my #room-info;
for #rooms -> $room {
my #room-authors;
my %room-authors;
my $room-count = 0;
for #(%books{$room}) -> $book {
my $count = $book.contains-word( $word );
if $count > 0 {
$total-count += $count;
$room-count += $count;
my $author = $book.author;
if %room-authors{$author}:exists {
$(%room-authors{$author}).update($book, $word, $count);
}
else {
%room-authors{$author} = Room-Author.new(
book => $book, word => $word, count => $count
);
#room-authors.push( $author );
}
}
}
if #room-authors.elems > 0 {
#room-info.push(
Room-Info.new(
room => $room, room-count => $room-count,
order => #room-authors, hash => %room-authors
)
);
}
}
say "Word: $word";
say "TOTAL: $total-count";
for #room-info -> $room {
my #room-authors = $room.order;
my %room-authors = $room.hash;
say $room.room ~ " : " ~ $room.room-count;
for #room-authors -> $author-str {
my $author = %room-authors{$author-str};
say " author: " ~ $author.name ~ " : " ~ $author.count;
for #($author.titles) -> $title {
say " title: " ~ $title.title ~ " : " ~ $title.count;
for #($title.pages) -> $page {
say " page_" ~ $page.page ~ ": " ~ $page.count;
}
}
}
}
Here the classes Page, Title, Room-Info, Book, and Room-Author could look like (note: more details must be filled in in real code):
class Page {
has Int $.page;
has Int $.count;
}
class Title {
has Str $.title;
has Page #.pages;
has Int $.count;
}
class Room-Info {
has $.room;
has $.room-count;
has #.order;
has %.hash;
}
class Book {
has Str $.author;
has Str $.title;
has Str $.text;
# checks how many times a word occurs in the book
method contains-word ( $word, --> Int ) {
return 2; # Stub, insert more code here..
}
method get-page-matches( $word ) {
return [Page.new(page => 50, count => 1),
Page.new(page => 150, count => 2)]; # Stub, insert more code..
}
}
class Room-Author {
has Title #.titles;
has Bool %!titles;
has $.name;
has $.count;
submethod BUILD(:$book, :$word, :$!count) {
my $title = $book.title;
$!name = $book.author;
%!titles{$title} = True;
#!titles.push(
Title.new(title => $title,
pages => $book.get-page-matches( $word ),
count => $!count,
)
);
}
method update( $book, $word, $count ) {
my $title = $book.title;
$!count += $count;
my $author = $book.author; # should be the same as $.name..
if %!titles{$title}:exists {
die "Unexpected: Duplicate title '$title' for $author";
}
else {
%!titles{$title} = True;
my Page #pages = $book.get-page-matches( $word );
#!titles.push(
Title.new(title => $title,
pages => $book.get-page-matches( $word ),
count => $count,
) );
}
}
}