<?php
/**
* CakePHP(tm) : Rapid Development Framework (https://cakephp.org)
* Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
*
* Licensed under The MIT License
* For full copyright and license information, please see the LICENSE.txt
* Redistributions of files must retain the above copyright notice.
*
* @copyright Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
* @link https://cakephp.org CakePHP(tm) Project
* @license https://opensource.org/licenses/mit-license.php MIT License
*/
namespace Cake\Collection\Iterator;
use ArrayIterator;
use IteratorAggregate;
use LogicException;
use Traversable;
/**
* Implements a simplistic version of the popular Map-Reduce algorithm. Acts
* like an iterator for the original passed data after each result has been
* processed, thus offering a transparent wrapper for results coming from any
* source.
*/
class MapReduce implements IteratorAggregate
{
/**
* Holds the shuffled results that were emitted from the map
* phase
*
* @var array
*/
protected $_intermediate = [];
/**
* Holds the results as emitted during the reduce phase
*
* @var array
*/
protected $_result = [];
/**
* Whether the Map-Reduce routine has been executed already on the data
*
* @var bool
*/
protected $_executed = false;
/**
* Holds the original data that needs to be processed
*
* @var \Traversable|null
*/
protected $_data;
/**
* A callable that will be executed for each record in the original data
*
* @var callable
*/
protected $_mapper;
/**
* A callable that will be executed for each intermediate record emitted during
* the Map phase
*
* @var callable|null
*/
protected $_reducer;
/**
* Count of elements emitted during the Reduce phase
*
* @var int
*/
protected $_counter = 0;
/**
* Constructor
*
* ### Example:
*
* Separate all unique odd and even numbers in an array
*
* ```
* $data = new \ArrayObject([1, 2, 3, 4, 5, 3]);
* $mapper = function ($value, $key, $mr) {
* $type = ($value % 2 === 0) ? 'even' : 'odd';
* $mr->emitIntermediate($value, $type);
* };
*
* $reducer = function ($numbers, $type, $mr) {
* $mr->emit(array_unique($numbers), $type);
* };
* $results = new MapReduce($data, $mapper, $reducer);
* ```
*
* Previous example will generate the following result:
*
* ```
* ['odd' => [1, 3, 5], 'even' => [2, 4]]
* ```
*
* @param \Traversable $data the original data to be processed
* @param callable $mapper the mapper callback. This function will receive 3 arguments.
* The first one is the current value, second the current results key and third is
* this class instance so you can call the result emitters.
* @param callable|null $reducer the reducer callback. This function will receive 3 arguments.
* The first one is the list of values inside a bucket, second one is the name
* of the bucket that was created during the mapping phase and third one is an
* instance of this class.
*/
public function __construct(Traversable $data, callable $mapper, callable $reducer = null)
{
$this->_data = $data;
$this->_mapper = $mapper;
$this->_reducer = $reducer;
}
/**
* Returns an iterator with the end result of running the Map and Reduce
* phases on the original data
*
* @return \ArrayIterator
*/
public function getIterator()
{
if (!$this->_executed) {
$this->_execute();
}
return new ArrayIterator($this->_result);
}
/**
* Appends a new record to the bucket labelled with $key, usually as a result
* of mapping a single record from the original data.
*
* @param mixed $val The record itself to store in the bucket
* @param string $bucket the name of the bucket where to put the record
* @return void
*/
public function emitIntermediate($val, $bucket)
{
$this->_intermediate[$bucket][] = $val;
}
/**
* Appends a new record to the final list of results and optionally assign a key
* for this record.
*
* @param mixed $val The value to be appended to the final list of results
* @param string|null $key and optional key to assign to the value
* @return void
*/
public function emit($val, $key = null)
{
$this->_result[$key === null ? $this->_counter : $key] = $val;
$this->_counter++;
}
/**
* Runs the actual Map-Reduce algorithm. This is iterate the original data
* and call the mapper function for each , then for each intermediate
* bucket created during the Map phase call the reduce function.
*
* @return void
* @throws \LogicException if emitIntermediate was called but no reducer function
* was provided
*/
protected function _execute()
{
$mapper = $this->_mapper;
foreach ($this->_data as $key => $val) {
$mapper($val, $key, $this);
}
$this->_data = null;
if (!empty($this->_intermediate) && empty($this->_reducer)) {
throw new LogicException('No reducer function was provided');
}
$reducer = $this->_reducer;
foreach ($this->_intermediate as $key => $list) {
$reducer($list, $key, $this);
}
$this->_intermediate = [];
$this->_executed = true;
}
}