Collection

• Overview
• Installation
• How to use
  • Writing
  • Filtering
  • Ordering
  • Retrieving
  • Comparing
  • Aggregation
  • Transforming
• FAQ
• License
• Contributing

Overview

The Collection library provides a flexible and efficient API to manipulate, iterate, and manage collections in a structured and type-safe manner.

It leverages PHP's Generators for optimized memory usage and lazy evaluation, ensuring that large datasets are handled efficiently without loading all elements into memory at once.

The library supports adding, removing, filtering, sorting, and transforming elements.

Installation

composer require tiny-blocks/collection

How to use

The library exposes the available behaviors through the Collectible interface and provides utilities to manipulate collections of various types.

Concrete implementation

The Collection class implements the Collectible interface and provides a concrete implementation for handling collections.

It allows for adding, removing, filtering, and sorting elements, as well as transforming them into different formats like arrays and JSON.

The class is designed to work with generic key-value pairs, ensuring type safety and flexibility for a variety of use cases.

<?php

declare(strict_types=1);

namespace Example;

use TinyBlocks\Collection\Collection;
use TinyBlocks\Collection\Order;
use TinyBlocks\Mapper\KeyPreservation;

$collection = Collection::createFrom(elements: [1, 2, 3, 4, 5])
    ->add(6, 7) 
    ->filter(predicates: static fn(int $value): bool => $value > 3) 
    ->sort(order: Order::ASCENDING_VALUE) 
    ->map(transformations: static fn(int $value): int => $value * 2) 
    ->toArray(keyPreservation: KeyPreservation::DISCARD); 

# Output: [8, 10, 12, 14]

Extending Collection

Domain collections should extend the Collection class to inherit all collection behavior:

<?php

declare(strict_types=1);

namespace Example;

use TinyBlocks\Collection\Collection;

final class Invoices extends Collection
{
    public function totalAmount(): float
    {
        return $this->reduce(
            accumulator: static fn(float $carry, Invoice $invoice): float => $carry + $invoice->amount,
            initial: 0.0
        );
    }
}

Writing

These methods enable adding, removing, and modifying elements in the Collection.

Adding elements

• add: Returns a new collection with the specified elements appended.

  $collection->add(1, 2, 3);

  $collection->add('X', 'Y', 'Z');

Merging collections

• merge: Merges the elements of another Collectible into the current Collection.

  $collectionA->merge(other: $collectionB);

Removing elements

• remove: Returns a new collection with all occurrences of the specified element removed.

  $collection->remove(element: 1);

• removeAll: Returns a new collection with elements removed.
  
  

  • With a predicate: Removes only the elements that satisfy the given predicate.

    $collection->removeAll(predicate: static fn(Amount $amount): bool => $amount->value > 10.0);

  • Without a predicate: Removes all elements from the Collection.

    $collection->removeAll();

Filtering

These methods enable filtering elements in the Collection based on specific conditions.

Filter by predicate

• filter: Retains only elements satisfying all given predicates.
  
  

  • With predicates: Retains elements that satisfy the provided predicates.

    $collection->filter(predicates: static fn(Amount $amount): bool => $amount->value > 100);

  • Without predicates: Removes all falsy values (e.g., null, false, 0, '', empty arrays).

    $collection->filter();

Ordering

These methods enable sorting elements in the Collection based on the specified order and optional comparator.

Sort by order and custom comparator

• sort: Returns a new sorted collection.

  Order::ASCENDING_KEY: Sorts the collection in ascending order by key.
  Order::DESCENDING_KEY: Sorts the collection in descending order by key.
  Order::ASCENDING_VALUE: Sorts the collection in ascending order by value.
  Order::DESCENDING_VALUE: Sorts the collection in descending order by value.
  

  By default, Order::ASCENDING_KEY is used.

  use TinyBlocks\Collection\Order;
        
  $collection->sort(order: Order::DESCENDING_VALUE);

  Sort the Collection using a custom comparator to determine how elements should be compared.

  use TinyBlocks\Collection\Order;
        
  $collection->sort(
      order: Order::ASCENDING_VALUE,
      comparator: static fn(Amount $first, Amount $second): int => $first->value <=> $second->value
  );

Retrieving

These methods allow access to elements within the Collection, such as fetching the first or last element, counting the elements, or finding elements that match a specific condition.

Retrieve count

• count: Returns the total number of elements in the Collection.

  $collection->count();

Check if empty

• isEmpty: Determines whether the collection has no elements.

  $collection->isEmpty();

Retrieve by condition

• findBy: Finds the first element that satisfies any given predicate, or returns null if no predicate matches. When called without predicates, it returns null.

  $collection->findBy(predicates: static fn(CryptoCurrency $crypto): bool => $crypto->symbol === 'ETH');

Retrieve single elements

• first: Retrieves the first element from the Collection or returns a default value if the Collection is empty.

  $collection->first(defaultValueIfNotFound: 'fallback');

• getBy: Retrieves an element by its zero-based index or returns a default value if the index is out of bounds.

  $collection->getBy(index: 0, defaultValueIfNotFound: 'fallback');

• last: Retrieves the last element from the Collection or returns a default value if the Collection is empty.

  $collection->last(defaultValueIfNotFound: 'fallback');

Retrieve collection segments

• slice: Extracts a contiguous segment of the collection, starting at the specified offset. If length is negative, it excludes that many elements from the end. If length is not provided or set to -1, it returns all elements from the specified offset to the end.

  $collection->slice(offset: 1, length: 2);

Comparing

These methods enable comparing collections to check for equality or to verify element membership.

Check if collection contains element

• contains: Checks if the Collection contains a specific element. Uses strict equality for scalars and loose equality for objects.

  $collection->contains(element: 5);

Compare collections for equality

• equals: Compares the current Collection with another collection for element-wise equality.

  $collectionA->equals(other: $collectionB);

Aggregation

These methods perform operations that return a single value based on the Collection's content, such as summing or combining elements.

• reduce: Combines all elements in the Collection into a single value using the provided accumulator function and an initial value. This method is helpful for accumulating results, like summing or concatenating values.

  $collection->reduce(
      accumulator: static fn(float $carry, float $amount): float => $carry + $amount,
      initial: 0.0
  );

• joinToString: Joins all elements into a string with the given separator.

  $collection->joinToString(separator: ', ');

Transforming

These methods allow the Collection's elements to be transformed or converted into different formats.

Applying actions without modifying elements

• each: Executes actions on each element in the Collection without modification. The method is helpful for performing side effects, such as logging or accumulating values.

  $collection->each(actions: static fn(Amount $amount): void => $total += $amount->value);

Grouping elements

• groupBy: Groups the elements in the Collection based on the provided classifier.

  $collection->groupBy(classifier: static fn(Amount $amount): string => $amount->currency->name);

Mapping elements

• map: Applies transformations to each element in the Collection and returns a new collection with the transformed elements.

  $collection->map(transformations: static fn(int $value): int => $value * 2);

Flattening elements

• flatten: Flattens nested iterables by exactly one level. Non-iterable elements are yielded as-is.

  $collection->flatten();

Convert to array

• toArray: Converts the Collection into an array.

  KeyPreservation::DISCARD: Converts while discarding the keys.
  KeyPreservation::PRESERVE: Converts while preserving the original keys.
  

  By default, KeyPreservation::PRESERVE is used.

  use TinyBlocks\Mapper\KeyPreservation;
  
  $collection->toArray(keyPreservation: KeyPreservation::DISCARD);

Convert to JSON

• toJson: Converts the Collection into a JSON string.

  KeyPreservation::DISCARD: Converts while discarding the keys.
  KeyPreservation::PRESERVE: Converts while preserving the original keys.
  

  By default, KeyPreservation::PRESERVE is used.

  use TinyBlocks\Mapper\KeyPreservation;
  
  $collection->toJson(keyPreservation: KeyPreservation::DISCARD);

FAQ

01. Why is my iterator consumed after certain operations?

The Collection class leverages PHP's Generators to provide lazy evaluation, meaning elements are only generated as needed.

It cannot be reused once a generator is consumed (i.e., after you iterate over it or apply certain operations).

This behavior is intended to optimize memory usage and performance but can sometimes lead to confusion when reusing an iterator after operations like count, toJson, or toArray.

02. How does lazy evaluation affect memory usage in Collection?

Lazy evaluation, enabled by PHP's Generators, allows Collection to handle large datasets without loading all elements into memory at once.

This results in significant memory savings when working with large datasets or performing complex chained operations.

However, this also means that some operations will consume the generator, and you cannot access the elements unless you recreate the Collection.

03. What is the difference between eager and lazy evaluation?

• Eager evaluation (createFrom / createFromEmpty): Elements are materialized immediately into an array, enabling constant-time access by index, count, and repeated iteration.

• Lazy evaluation (createLazyFrom / createLazyFromEmpty): Elements are processed on-demand through generators, consuming memory only as each element is yielded. Ideal for large datasets or pipelines where not all elements need to be materialized.

License

Collection is licensed under MIT.

Contributing

Please follow the contributing guidelines to contribute to the project.