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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.

Namespace: Cake\Collection\Iterator

Property Summary

  • $_counter protected
    int

    Count of elements emitted during the Reduce phase

  • $_data protected
    Traversable|null

    Holds the original data that needs to be processed

  • $_executed protected
    bool

    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

  • __construct() public

    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.

  • emitIntermediate() public

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

  • getIterator() public

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

Method Detail

__construct() ¶ public

__construct(Traversable $data, callable $mapper, callable|null $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|null $reducer optional

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() ¶ protected

_execute(): void

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.

Returns
void
Throws
LogicException
if emitIntermediate was called but no reducer function was provided

emit() ¶ public

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

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

and optional key to assign to the value

Returns
void

emitIntermediate() ¶ public

emitIntermediate(mixed $val, string $bucket): void

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

Returns
void

getIterator() ¶ public

getIterator(): ArrayIterator

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

Returns
ArrayIterator

Property Detail

$_counter ¶ protected

Count of elements emitted during the Reduce phase

Type
int

$_data ¶ protected

Holds the original data that needs to be processed

Type
Traversable|null

$_executed ¶ protected

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

Type
bool

$_intermediate ¶ protected

Holds the shuffled results that were emitted from the map phase

Type
array

$_mapper ¶ protected

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

Type
callable

$_reducer ¶ protected

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

Type
callable|null

$_result ¶ protected

Holds the results as emitted during the reduce phase

Type
array
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