NAME

autobox::Transform - Autobox methods to transform Arrays and Hashes

SYNOPSIS

# These are equivalent ways to transform arrays and arrayrefs

### map_by
my @genres = map { $_->genre() } @$books;
my @genres = $books->map_by("genre");

my $genres = [ map { $_->genre() } @$books ];
my $genres = $books->map_by("genre");

# With sum from autobox::Core / List::AllUtils
my $book_order_total = sum(
    map { $_->price_with_tax($tax_pct) } @{$order->books}
);
my $book_order_total = $order->books
    ->map_by(price_with_tax => [$tax_pct])->sum;


### grep_by
my $sold_out_books = [ grep { $_->is_sold_out } @$books ];
my $sold_out_books = $books->grep_by("is_sold_out");

my $books_in_library = [ grep { $_->is_in_library($library) } @$books ];
my $books_in_library = $books->grep_by(is_in_library => [$library]);


### group_by

$books->group_by("title"),
# {
#     "Leviathan Wakes"       => $books->[0],
#     "Caliban's War"         => $books->[1],
#     "The Tree-Body Problem" => $books->[2],
#     "The Name of the Wind"  => $books->[3],
# },

$authors->group_by(publisher_affiliation => ["with"]),
# {
#     'James A. Corey with Orbit'     => $authors->[0],
#     'Cixin Liu with Head of Zeus'   => $authors->[1],
#     'Patrick Rothfuss with Gollanz' => $authors->[2],
# },

$books->group_by_count("genre"),
# {
#     "Sci-fi"  => 3,
#     "Fantasy" => 1,
# },

my $genre_books = $books->group_by_array("genre");
# {
#     "Sci-fi"  => [ $sf_book_1, $sf_book_2, $sf_book_3 ],
#     "Fantasy" => [ $fantasy_book_1 ],
# },


#### flat
my $prolific_author_books = [ map { @{$_->books} } @$authors ]
my $prolific_author_books = $authors->map_by("books")->flat

DESCRIPTION

Note: This module supercedes autobox::Array::Transform which was unfortunately named.

High level autobox methods you can call on arrays, arrayrefs, hashes and hashrefs e.g. map_by(), grep_by(), group_by()

Raison d'etre

autobox::Core is awesome, for a variety of reasons.

  • It cuts down on dereferencing punctuation clutter.
  • It makes map and grep transforms read in the same direction it's executed.
  • It makes it easier to write those things in a natural order. No need to move the cursor around a lot just to fix dereferencing, order of operations etc.

autobox::Transform provides a few higher level methods for mapping, greping and sorting common cases which are easier to read and write.

Since they are at a slightly higher semantic level, once you know them they also provide a more specific meaning than just "map" or "grep".

(Compare the difference between seeing a "map" and seeing a "foreach" loop. Just seeing the word "map" hints at what type of thing is going on here: transforming a list into another list).

The methods of autobox::Transform are not suitable for all cases, but when used appropriately they will lead to much more clear, succinct and direct code, especially in conjunction with autobox::Core.

Examples

my $total_order_amount = $order->books
    ->map_by(price_with_tax => [ $tax_pct ])
    ->sum;

my $order_authors = $order->books
    ->map_by("author")
    ->map_by("name")->uniq->sort->join(", ");

List and Scalar Context

All of the methods below are context sensitive, i.e. they return a list in list context and an arrayref in scalar context, just like autobox::Core.

When in doubt, assume they work like map and grep, and convert the return value to references where you might have an unobvious list context. E.g.

$self->my_method(
    # Wrong, this is list context and wouldn't return an arrayref
    books => $books->grep_by("is_published"),
),

$self->my_method(
    # Correct, convert the list to an arrayref
    books => [ $books->grep_by("is_published") ],
),
$self->my_method(
    # Correct, ensure scalar context i.e. an array ref
    books => scalar $books->grep_by("is_published"),
),

AUTOBOX ARRAY METHODS

map_by($method, @$args?) : @array | @$array

Call the $method on each item in the list. Like:

map { $_->$method() }

Examples:

my @ahthor_names = $authors->map_by("name");
my $author_names = @publishers->map_by("authors")->map_by("name");

Optionally pass in @$args in the method call. Like:

map { $_->$method(@$args) }

Examples:

my @prices_including_tax = $books->map_by("price_with_tax", [ $tax_pct ]);
my $prices_including_tax = $books->map_by(price_with_tax => [ $tax_pct ]);

grep_by($method, @$args?) : @array | @$array

Call the $method on each item in the list. Like:

grep { $_->$method() }

Examples:

my @prolific_authors = $authors->grep_by("is_prolific");

Optionally pass in @$args in the method call. Like:

grep { $_->$method(@$args) }

Examples:

my @books_to_charge_for = $books->grep_by("price_with_tax", [ $tax_pct ]);

group_by($method, @$args = [], $value_sub = object) : %key_value | %$key_value

Call ->$method(@$args) on each object in the array (just like ->map_by) and group the return values as keys in a hashref.

The default $value_sub puts the objects in the list as the hash values.

Example:

my $title_book = $books->group_by("title");
# {
#     "Leviathan Wakes"       => $books->[0],
#     "Caliban's War"         => $books->[1],
#     "The Tree-Body Problem" => $books->[2],
#     "The Name of the Wind"  => $books->[3],
# },

The $value_sub

This is a bit tricky to use, so the most common thing would probably be to use one of the more specific group_by-methods which do common things (see below). It should be capable enough to achieve what you need though, so here's how it works:

The hash key is whatever is returned from $object->$method(@$args).

The hash value is whatever is returned from

my $new_value = $value_sub->($current_value, $object, $key);

where:

  • $current value is the current hash value for this key (or undef if the first one).
  • $object is the current item in the list. The current $_ is also set to this.
  • $key is the key returned by $object->$method(@$args)

group_by_count($method, @$args = []) : %key_count | %$key_count

Just like group_by, but the hash values are the the number of instances each $method value occurs in the list.

Example:

$books->group_by_count("genre"),
# {
#     "Sci-fi"  => 3,
#     "Fantasy" => 1,
# },

$book->genre() returns the genre string. There are three books counted for the "Sci-fi" key.

group_by_array($method, @$args = []) : %key_objects | %$key_objects

Just like group_by, but the hash values are arrayrefs containing the objects which has each $method value.

Example:

my $genre_books = $books->group_by_array("genre");
# {
#     "Sci-fi"  => [ $sf_book_1, $sf_book_2, $sf_book_3 ],
#     "Fantasy" => [ $fantasy_book_1 ],
# },

$book->genre() returns the genre string. The three Sci-fi book objects are collected under the Sci-fi key.

flat() : @array | @$array

Return a flattened array, assuming the array items themselves are array refs. I.e.

[
    [ 1, 2, 3 ],
    [ "a", "b" ],
]->flat

returns

[ 1, 2, 3, "a", "b "]

This is useful if e.g. a map_by("some_method") returns arrayrefs of objects which you want to do further method calls on. Example:

# ->books returns an arrayref of Book objects with a ->title
$authors->map_by("books")->flat->map_by("title")

Note: This is different from autobox::Core's ->flatten, which reurns a list rather than an array and therefore can't be used in this way.

DEVELOPMENT

Author

Johan Lindstrom, <johanl [AT] cpan.org>

Source code

https://github.com/jplindstrom/p5-autobox-Transform

Bug reports

Please report any bugs or feature requests on GitHub:

https://github.com/jplindstrom/p5-autobox-Transform/issues.

COPYRIGHT & LICENSE

Copyright 2016- Johan Lindstrom, All Rights Reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.