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Class MapReduce

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.

Cake\Collection\Iterator\MapReduce implements IteratorAggregate
Namespace: Cake\Collection\Iterator
Location: Collection/Iterator/MapReduce.php

Properties summary

  • $_counter protected
    integer
    Count of elements emitted during the Reduce phase
  • $_data protected
    Traversable|null
    Holds the original data that needs to be processed
  • $_executed protected
    boolean
    Whether the Map-Reduce routine has been executed already on the data
  • $_intermediate protected
    array

    Holds the shuffled results that were emitted from the map phase

  • $_mapper protected
    callable
    A callable that will be executed for each record in the original data
  • $_reducer protected
    callable|null

    A callable that will be executed for each intermediate record emitted during the Map phase

  • $_result protected
    array
    Holds the results as emitted during the reduce phase

Method Summary

  • Constructor
  • _execute() protected

    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.

  • emit() public

    Appends a new record to the final list of results and optionally assign a key for this record.

  • Appends a new record to the bucket labelled with $key, usually as a result of mapping a single record from the original data.

  • Returns an iterator with the end result of running the Map and Reduce phases on the original data

Method Detail

__construct()source public

__construct( Traversable $data , callable $mapper , callable $reducer = null )

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]]

Parameters

Traversable $data
the original data to be processed
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.

callable $reducer optional null

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.

_execute()source protected

_execute( )

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.

Throws

LogicException

if emitIntermediate was called but no reducer function was provided


emit()source public

emit( mixed $val , string|null $key = null )

Appends a new record to the final list of results and optionally assign a key for this record.

Parameters

mixed $val
The value to be appended to the final list of results
string|null $key optional null
and optional key to assign to the value

emitIntermediate()source public

emitIntermediate( mixed $val , string $bucket )

Appends a new record to the bucket labelled with $key, usually as a result of mapping a single record from the original data.

Parameters

mixed $val
The record itself to store in the bucket
string $bucket
the name of the bucket where to put the record

getIterator()source public

getIterator( )

Returns an iterator with the end result of running the Map and Reduce phases on the original data

Returns

ArrayIterator

Implementation of

IteratorAggregate::getIterator()

Properties detail

$_countersource

protected integer

Count of elements emitted during the Reduce phase

$_datasource

protected Traversable|null

Holds the original data that needs to be processed

$_executedsource

protected boolean

Whether the Map-Reduce routine has been executed already on the data

false

$_intermediatesource

protected array

Holds the shuffled results that were emitted from the map phase

[]

$_mappersource

protected callable

A callable that will be executed for each record in the original data

$_reducersource

protected callable|null

A callable that will be executed for each intermediate record emitted during the Map phase

$_resultsource

protected array

Holds the results as emitted during the reduce phase

[]

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https://api.cakephp.org/3.8/class-Cake.Collection.Iterator.MapReduce.html