NAME

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

CONTEXT

autobox provides the ability to call methods on native types, e.g. strings, arrays, and hashes as if they were objects.

autobox::Core provides the basic methods for Perl core functions like uc, map, and grep.

This module, autobox::Transform, provides higher level and more specific methods to transform and manipulate arrays and hashes, in particular when the values are hashrefs or objects.

SYNOPSIS

use autobox::Core;  # map, uniq, sort, join, sum, etc.
use autobox::Transform;

Arrays

# use autobox::Core for ->map etc.

# filter (grep)
$book_locations->filter(); # true values
$books->filter(sub { $_->is_in_library($library) });
$book_names->filter( qr/lord/i );
$book_types->filter("scifi");
$book_types->filter({ fantasy => 1, scifi => 1 }); # hash key exists

# Flatten arrayrefs-of-arrayrefs
$authors->map_by("books") # ->books returns an arrayref
# [ [ $book1, $book2 ], [ $book3 ] ]
$authors->map_by("books")->flat;
# [ $book1, $book2, $book3 ]

# Return reference, even in list context, e.g. in a parameter list
$book_locations->filter()->to_ref;

# Return array, even in scalar context
@books->to_array;

Arrays with hashrefs/objects

# $books and $authors below are arrayrefs with either objects or
# hashrefs (the call syntax is the same)

$books->map_by("genre");
$books->map_by([ price_with_tax => $tax_pct ]);

$books->filter_by("is_sold_out");
$books->filter_by([ is_in_library => $library ]);
$books->filter_by([ price_with_tax => $rate ], sub { $_ > 56.00 });
$books->filter_by("price", sub { $_ > 56.00 });
$books->filter_by("author", "James A. Corey");
$books->filter_by("author", qr/corey/i);

# grep_by is an alias for filter_by
$books->grep_by("is_sold_out");

$books->uniq_by("id");

$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 ],
# },

Hashes

# Upper-case the genre name, and make the count say "n books"
$genre_count->map_each(sub { uc( $_[0] ) => "$_ books" });
# {
#     "FANTASY" => "1 books",
#     "SCI-FI"  => "3 books",
# },

# Make the count say "n books"
$genre_count->map_each_value(sub { "$_ books" });
# {
#     "Fantasy" => "1 books",
#     "Sci-fi"  => "3 books",
# },

# Transform each pair to the string "n: genre"
$genre_count->map_each_to_array(sub { "$_: $_[0]" });
# [ "1: Fantasy", "3: Sci-fi" ]

# Return reference, even in list context, e.g. in a parameter list
%genre_count->to_ref );

# Return hash, even in scalar context
$author->book_count->to_hash;

Combined examples

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

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

DESCRIPTION

High level autobox methods you can call on arrays, arrayrefs, hashes and hashrefs.

$array->filter()
$array->flat()
$array->as_ref()
$array->as_array()
$array->map_by()
$array->filter_by()
$array->uniq_by()
$array->group_by()
$array->group_by_count()
$array->group_by_array()

$hash->map_each
$hash->map_each_value
$hash->map_each_to_array
$array->as_ref()
$array->as_hash()

Transforming lists of objects vs list of hashrefs

map_by, filter_by etc. (all methods named *_by) work with sets of hashrefs or objects.

These methods are called the same way regardless of whether the array contains objects or hashrefs. The items in the list must all be either objects or hashrefs.

If the array contains objects, a method is called on each object (possibly with the arguments provided).

If the array contains hashrefs, the hash key is looked up on each item.

Calling accessor methods with arguments

Consider filter_by:

$array->filter_by($accessor, $predicate)

If the $accessor is a string, it's a simple lookup/method call.

# method call without args
$books->filter_by("price", sub { $_ < 15.0 })
# becomes $_->price() or $_->{price}

If the $accessor is an arrayref, the first item is the method name, and the rest of the items are the arguments to the method.

# method call with args
$books->filter_by([ price_with_discount => 5.0 ], sub { $_ < 15.0 })
# becomes $_->price_with_discount(5.0)

Deprecated syntax

There is an older syntax for calling methods with arguments. It was abandoned to open up more powerful ways to use grep/filter type methods. Here it is for reference, in case you run into existing code.

$array->filter_by($accessor, $args, $subref)
$books->filter_by("price_with_discount", [ 5.0 ], sub { $_ < 15.0 })

Call the method $accessor on each object using the arguments in the $args arrayref like so:

$object->$accessor(@$args)

This style is deprecated, and planned for removal in version 2.000, so if you have code with the old call style, please:

Replace your existing code with the new style as soon as possible. The change is trivial and the code easily found by grep/ack.
If need be, pin your version to < 2.000 in your cpanfile, dist.ini or whatever you use to avoid upgrading to an incompatible version.

Filter predicates

There are several methods that filter items, e.g. filter (duh), and filter_by. These methods take a $predicate argument, to determine which items to retain or filter out.

If $predicate is an unblessed scalar, it is compared to each value with string eq.

$books->filter_by("author", "James A. Corey");

If $predicate is a regex, it is compared to each value with =~.

$books->filter_by("author", qr/Corey/);

If $predicate is a hashref, values in @array are retained if the $predicate hash key exists (the hash values are irrelevant).

$books->filter_by(
    "author", {
        "James A. Corey"   => undef,
        "Cixin Liu"        => 0,
        "Patrick Rothfuss" => 1,
    },
);

If $predicate is a subref, the subref is called for each value to check whether this item should remain in the list.

The $filter_subref should return a true value to remain. $_ is set to the current $value.

$authors->filter_by(publisher => sub { $_->name =~ /Orbit/ });

List and Scalar Context

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

Beware: you might be in list context when you need an arrayref.

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->filter_by("is_published"),
);

$self->my_method(
    # Correct, convert the returned list to an arrayref
    books => [ $books->filter_by("is_published") ],
);
$self->my_method(
    # Correct, ensure scalar context to get an array ref
    books => scalar $books->filter_by("is_published"),
);

# Probably the nicest, since it goes at the end
$self->my_method(
    # Correct, use ->to_ref to ensure an array reference is returned
    books => $books->filter_by("is_published")->to_ref,
);

METHODS ON ARRAY

@array->filter($predicate = is_true_subref) : @array | @$array

Similar to Perl's grep, return an @array with values for which $predicate yields a true value.

$predicate can be a subref, string, undef, regex, or hashref. See "Filter predicates".

The default (no $predicate) is a subref which retains true values in the @array.

Examples:

my @apples     = $fruit->filter("apple");
my @any_apple  = $fruit->filter( qr/apple/i );
my @publishers = $authors->filter(
    sub { $_->publisher->name =~ /Orbit/ },
);

filter and grep

autobox::Core's grep method takes a subref, just like this method. filter also supports the other predicate types, like string, regex, etc.

@array->flat() : @array | @$array

Return a (one level) flattened array, assuming the array items themselves are array refs. I.e.

[
    [ 1, 2, 3 ],
    [ "a", "b" ],
    [ [ 1, 2 ], { 3 => 4 } ]
]->flat

returns

[ 1, 2, 3, "a", "b ", [ 1, 2 ], { 3 => 4 } ]

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.

@array->to_ref() : $arrayref

Return the reference to the @array, regardless of context.

Useful for ensuring the last array method return a reference while in scalar context. Typically:

do_stuff(
    books => $author->map_by("books")->to_ref,
);

map_by is called in list context, so without ->to_ref it would have return an array, not an arrayref.

@array->to_array() : @array

Return the @array, regardless of context. This is mostly useful if called on a ArrayRef at the end of a chain of method calls.

METHODS ON ARRAY-OF-OBJECTS/HASHES

@array->map_by($accessor) : @array | @$array

$accessor is either a string, or an arrayref where the first item is a string.

Call the $accessor on each object in @array, or get the hash key value on each hashref in @array. Like:

map { $_->$accessor() }
# or
map { $_->{$accessor} }

Examples:

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

Or get the hash key value. Example:

my @review_scores = $reviews->map_by("score");

Alternatively the $accessor is an arrayref. The first item is the accessor name, and the rest of the items are passed as args the method call. This only works when working with objects, not with hashrefs.

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 ]);

@array->filter_by($accessor, $predicate = is_true_subref) : @array | @$array

$accessor is either a string, or an arrayref where the first item is a string.

Call the $accessor on each object in the list, or get the hash key value on each hashref in the list.

Example:

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

Example:

my @books_to_charge_for = $books->filter_by([ price_with_tax => $tax_pct ]);

Use the $predicate to determine whether the value should remain. $predicate can be a subref, string, undef, regex, or hashref. See "Filter predicates".

The default (no $predicate) is a subref which retains true values in the result @array.

Examples:

# Custom predicate subref
my @authors = $authors->filter_by(
    "publisher",
    sub { $_->name =~ /Orbit/ },
);

# Call method with args and match a regex
my @authors = $authors->filter_by(
    [ publisher_affiliation => "with" ],
    qr/Orbit/ },
);

Note: if you do something complicated with a $predicate subref, it might be easier and more readable to simply use $array-$<gtfilter()>.

Alias

grep_by is an alias for filter_by. Unlike grep vs filter, this one works exaclty the same way.

@array->uniq_by($accessor) : @array | @$array

$accessor is either a string, or an arrayref where the first item is a string.

Call the $accessor on each object in the list, or get the hash key value on each hashref in the list. Return list of items wich have a unique set of return values. The order is preserved. On duplicates, keep the first occurrence.

Examples:

# You have gathered multiple Author objects with duplicate ids
my @authors = $authors->uniq_by("author_id");

Examples:

my @example_book_at_price_point = $books->uniq_by(
    [ price_with_tax => $tax_pct ],
);

@array->group_by($accessor, $value_subref = object) : %key_value | %$key_value

$accessor is either a string, or an arrayref where the first item is a string.

Call ->$accessor on each object in the array, or get the hash key for each hashref in the array (just like ->map_by) and group the values as keys in a hashref.

The default $value_subref puts each object in the list as the hash value. If the key is repeated, the value is overwritten with the last object.

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_subref

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 (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 $object->$accessor.

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 $object->$accessor(@$args)

@array->group_by_count($accessor) : %key_count | %$key_count

$accessor is either a string, or an arrayref where the first item is a string.

Just like group_by, but the hash values are the the number of instances each $accessor 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.

@array->group_by_array($accessor) : %key_objects | %$key_objects

$accessor is either a string, or an arrayref where the first item is a string.

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

METHODS ON HASH

%hash->map_each($key_value_subref) : %new_hash | %$new_hash

Map each key-value pair in the hash using the $key_value_subref. Similar to how to how map transforms a list into another list, map_each transforms a hash into another hash.

$key_value_subref->($key, $value) is called for each pair (with $_ set to the value).

The subref should return an even-numbered list with zero or more key-value pairs which will make up the %new_hash. Typically two items are returned in the list (the key and the value).

Example

{ a => 1, b => 2 }->map_each(sub { "$_[0]$_[0]" => $_ * 2 });
# Returns { aa => 2, bb => 4 }

%hash->map_each_value($value_subref) : %new_hash | %$new_hash

Map each value in the hash using the $value_subref, but keep the keys the same.

$value_subref->($key, $value) is called for each pair (with $_ set to the value).

The subref should return a single value for each key which will make up the %new_hash (with the same keys but with new mapped values).

Example

{ a => 1, b => 2 }->map_each_value(sub { $_ * 2 });
# Returns { a => 2, b => 4 }

%hash->map_each_to_array($item_subref) : @new_array | @$new_array

Map each key-value pair in the hash into a list using the $item_subref.

$item_subref->($key, $value) is called for each pair (with $_ set to the value) in key order.

The subref should return zero or more list items which will make up the @new_array. Typically one item is returned.

Example

{ a => 1, b => 2 }->map_each_to_array(sub { "$_[0]-$_" });
# Returns [ "a-1", "b-2" ]

%hash->to_ref() : $hashref

Return the reference to the %hash, regardless of context.

Useful for ensuring the last hash method return a reference while in scalar context. Typically:

do_stuff(
    genre_count => $books->group_by_count("genre")->to_ref,
);

%hash->to_hash() : %hash

Return the %hash, regardless of context. This is mostly useful if called on a HashRef at the end of a chain of method calls.

AUTOBOX AND VANILLA PERL

Raison d'etre

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

It cuts down on dereferencing punctuation clutter, both by using methods on references and by using ->elements to deref arrayrefs.
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.

On top of this, autobox::Transform provides a few higher level methods for mapping, filtering 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.

Code Comparison

These examples are only for when there's a straightforward and simple Perl equivalent.

### map_by - method call: $books are Book objects
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;

### map_by - hash key: $books are book hashrefs
my @genres = map { $_->{genre} } @$books;
my @genres = $books->map_by("genre");



### filter_by - method call: $books are Book objects
my $sold_out_books = [ grep { $_->is_sold_out } @$books ];
my $sold_out_books = $books->filter_by("is_sold_out");
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->filter_by([ is_in_library => $library ]);

### filter_by - hash key: $books are book hashrefs
my $sold_out_books = [ grep { $_->{is_sold_out} } @$books ];
my $sold_out_books = $books->filter_by("is_sold_out");



### uniq_by - method call: $books are Book objects
my %seen; my $distinct_books = [ grep { ! %seen{ $_->id // "" }++ } @$books ];
my $distinct_books = $books->uniq_by("id");

### uniq_by - hash key: $books are book hashrefs
my %seen; my $distinct_books = [ grep { ! %seen{ $_->{id} // "" }++ } @$books ];
my $distinct_books = $books->uniq_by("id");


#### flat - $author->books returns an arrayref of Books
my $author_books = [ map { @{$_->books} } @$authors ]
my $author_books = $authors->map_by("books")->flat

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

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

To install autobox::Transform, copy and paste the appropriate command in to your terminal.

cpanm

cpanm autobox::Transform

CPAN shell

perl -MCPAN -e shell
install autobox::Transform

For more information on module installation, please visit the detailed CPAN module installation guide.

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NAME

CONTEXT

SYNOPSIS

Arrays

Arrays with hashrefs/objects

Hashes

Combined examples

DESCRIPTION

Transforming lists of objects vs list of hashrefs

Calling accessor methods with arguments

Deprecated syntax

Filter predicates

List and Scalar Context

METHODS ON ARRAY

@array->filter($predicate = *is_true_subref*) : @array | @$array

filter and grep

@array->flat() : @array | @$array

@array->to_ref() : $arrayref

@array->to_array() : @array

METHODS ON ARRAY-OF-OBJECTS/HASHES

@array->map_by($accessor) : @array | @$array

@array->filter_by($accessor, $predicate = *is_true_subref*) : @array | @$array

Alias

@array->uniq_by($accessor) : @array | @$array

@array->group_by($accessor, $value_subref = object) : %key_value | %$key_value

The $value_subref

@array->group_by_count($accessor) : %key_count | %$key_count

@array->group_by_array($accessor) : %key_objects | %$key_objects

METHODS ON HASH

%hash->map_each($key_value_subref) : %new_hash | %$new_hash

Example

%hash->map_each_value($value_subref) : %new_hash | %$new_hash

Example

%hash->map_each_to_array($item_subref) : @new_array | @$new_array

Example

%hash->to_ref() : $hashref

%hash->to_hash() : %hash

AUTOBOX AND VANILLA PERL

Raison d'etre

Code Comparison

DEVELOPMENT

Author

Source code

Bug reports

COPYRIGHT & LICENSE

Module Install Instructions

@array->filter($predicate = is_true_subref) : @array | @$array

@array->filter_by($accessor, $predicate = is_true_subref) : @array | @$array