Elep

Introduction
============

Doctrine Collections is a library that contains classes for working with
arrays of data. Here is an example using the simple
``Doctrine\Common\Collections\ArrayCollection`` class:

.. code-block:: php
    <?php

use Doctrine\Common\Collections\ArrayCollection;

$collection = new ArrayCollection([1, 2, 3]);

$filteredCollection = $collection->filter(function($element) {
        return $element > 1;
    }); // [2, 3]

Collection Methods
==================

Doctrine Collections provides an interface named ``Doctrine\Common\Collections\Collection``
that resembles the nature of a regular PHP array. That is,
it is essentially an **ordered map** that can also be used
like a list.

A Collection has an internal iterator just like a PHP array. In addition,
a Collection can be iterated with external iterators, which is preferable.
To use an external iterator simply use the foreach language construct to
iterate over the collection, which calls ``getIterator()`` internally, or
explicitly retrieve an iterator though ``getIterator()`` which can then be
used to iterate over the collection. You can not rely on the internal iterator
of the collection being at a certain position unless you explicitly positioned it before.

Methods that do not alter the collection or have template types
appearing in invariant or contravariant positions are not directly
defined in ``Doctrine\Common\Collections\Collection``, but are inherited
from the ``Doctrine\Common\Collections\ReadableCollection`` interface.

The methods available on the interface are:

add
---

Adds an element at the end of the collection.

.. code-block:: php
    $collection->add('test');

clear
-----

Clears the collection, removing all elements.

.. code-block:: php
    $collection->clear();

contains
--------

Checks whether an element is contained in the collection. This is an O(n) operation, where n is the size of the collection.

.. code-block:: php
    $collection = new Collection(['test']);

$contains = $collection->contains('test'); // true

containsKey
-----------

Checks whether the collection contains an element with the specified key/index.

.. code-block:: php
    $collection = new Collection(['test' => true]);

$contains = $collection->containsKey('test'); // true

current
-------

Gets the element of the collection at the current iterator position.

.. code-block:: php
    $collection = new Collection(['first', 'second', 'third']);

$current = $collection->current(); // first

get
---

Gets the element at the specified key/index.

.. code-block:: php
    $collection = new Collection([
        'key' => 'value',
    ]);

$value = $collection->get('key'); // value

getKeys
-------

Gets all keys/indices of the collection.

.. code-block:: php
    $collection = new Collection(['a', 'b', 'c']);

$keys = $collection->getKeys(); // [0, 1, 2]

getValues
---------

Gets all values of the collection.

.. code-block:: php
    $collection = new Collection([
        'key1' => 'value1',
        'key2' => 'value2',
        'key3' => 'value3',
    ]);

$values = $collection->getValues(); // ['value1', 'value2', 'value3']

isEmpty
-------

Checks whether the collection is empty (contains no elements).

.. code-block:: php
    $collection = new Collection(['a', 'b', 'c']);

$isEmpty = $collection->isEmpty(); // false

first
-----

Sets the internal iterator to the first element in the collection and returns this element.

.. code-block:: php
    $collection = new Collection(['first', 'second', 'third']);

$first = $collection->first(); // first

exists
------

Tests for the existence of an element that satisfies the given predicate.

.. code-block:: php
    $collection = new Collection(['first', 'second', 'third']);

$exists = $collection->exists(function($key, $value) {
        return $value === 'first';
    }); // true

filter
------

Returns all the elements of this collection for which your callback function returns `true`.
The order and keys of the elements are preserved.