Class MapReduce

__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

if emitIntermediate was called but no reducer function was provided

emit()source public

emit( mixed $value , string|null $key null )

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

Parameters

mixed $value

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 $value , 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 $value

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

Implementation of