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
Properties summary
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$_counterprotectedintegerCount of elements emitted during the Reduce phase -
$_dataprotectedTraversable|nullHolds the original data that needs to be processed -
$_executedprotectedbooleanWhether the Map-Reduce routine has been executed already on the data -
$_intermediateprotectedarrayHolds the shuffled results that were emitted from the map phase
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$_mapperprotectedcallableA callable that will be executed for each record in the original data -
$_reducerprotectedcallable|nullA callable that will be executed for each intermediate record emitted during the Map phase
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$_resultprotectedarrayHolds the results as emitted during the reduce phase
Method Summary
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__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.
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emit() public
Appends a new record to the final list of results and optionally assign a key for this record.
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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.
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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 $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() 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() 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() 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() public ¶
getIterator( )
Returns an iterator with the end result of running the Map and Reduce phases on the original data
Returns
Implementation of
IteratorAggregate::getIterator()Properties detail
$_executed ¶
Whether the Map-Reduce routine has been executed already on the data
false