Map, Filter, and Reduce in PHP

@DerekB_WI
Map, Filter, and
Reduce in PHP
Presented by Derek Binkley

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@DerekB_WI
About Me
• Father of 3, Husband

• Software Consultant with Spark Labs

• PHP, Java, Groovy, JavaScript …

• He/Him/His

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@DerekB_WI

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@DerekB_WI
Google in 2004
• MapReduce: Simpliﬁed Data Processing on Large
Clusters, Jeﬀrey Dean and Sanjay Ghemawat

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–Oscar Stiﬀelman - early Google engineer
“Only when something is simple can you make it
really efﬁcient”

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@DerekB_WI
Java Data Streams
List numbers = Arrays.asList(5, 22, 457, 111233, 6);

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@DerekB_WI
Java Data Streams
List ﬁlteredNumbers = (List) numbers.stream()

.ﬁlter(num -> (int)num > 10)

.sorted()

.map(num -> (int)num * -1)

.collect(Collectors.toList());

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@DerekB_WI
Java Data Streams
Integer sum = numbers.stream()

.reduce(0, (subtotal, element) -> subtotal + element);

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@DerekB_WI
Java Data Streams
List ﬁlteredNumbers = (List) numbers.parallelStream()

.ﬁlter(num -> (int)num > 10)

.sorted()

.map(num -> (int)num * -1)

.collect(Collectors.toList());
Integer sum = numbers.parallelStream()

.reduce(0, (subtotal, element) -> subtotal + element);

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@DerekB_WI
JavaScript Promise
function loadImage() {

let imageUrl = 'https://live.staticﬂickr.com/
65535/47813616341_6063c7b420_b_d.jpg';

fetch(imageUrl)

.then((data) => {

// Save image and display

...

})

.catch((error) => {

// Alert user of error

...

});

}

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@DerekB_WI
Beneﬁts
• No Parallel Processing, So what else?

• Functional, no side-eﬀects

• Easy to read

• Single Responsibility

• Reduce boilerplate

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@DerekB_WI
Traditional Foreach
$placesArray = $reader->getFileContents(); 
 
$ﬁlteredLocations = [];

foreach ($placesArray as $place) { 
if ($place['state'] == 'AK') { 
$ﬁlteredLocations[] = new Place($place); 
} 
}

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@DerekB_WI
Filter
$placesArray = $reader->getFileContents();

$ﬁlteredAlaskaList = array_ﬁlter($placesArray, 
function($place) { 
return $place['state'] == 'AK'; 
} 
);

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@DerekB_WI
Filter - 7.4

$ﬁlteredAlaskaList = array_ﬁlter($placesArray, 
fn($place) => $place['state'] == 'AK' 
);

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@DerekB_WI
Traditional Foreach
$placesArray = $reader->getFileContents(); 
 
$ﬁlteredLocations = [];

foreach ($placesArray as $place) { 
if ($place['state'] == 'AK') { 
$ﬁlteredLocations[] = new Place($place); 
} 
}

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@DerekB_WI
Map

$modiﬁedList = array_map(

return PlaceMapper::parse($place); 
},  
$placesArray);

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@DerekB_WI
Map - 7.4

$ﬁlteredAlaskaList = array_map( 
fn($place) => PlaceMapper::parse($place),  
$placesArray);

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@DerekB_WI
Reduce
$myTrips = [ 
new Trip("name" => "school", "distance" => 1.5), 
new Trip("name" => "the store", "distance" => 2.5)];

$totalDriven = array_reduce($myTrips, 
function ($total, $trip) { 
return $total + $trip->distance; 
}, 
0 // initial 
);

echo "I biked {$totalDriven} kilometers today.";

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@DerekB_WI
Reduce - 7.4
$totalDriven = array_reduce($myTrips, 
fn($total, $trip) => $total + $trip->distance, 
0);

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@DerekB_WI
Traditional Loop
for ($i = 0; $i < count($placesArray); $i++) { 
$stateName = $placesArray[$i]['state'];

if (!array_key_exists($stateName, $stateCounters))  
{ 
$stateCounters[$stateName] = 0; 
}

$stateCounters[$stateName]++;

}

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@DerekB_WI
Reduce
$stateCounters = array_reduce($placesArray, 
function($totals, $location) { 
$totals[$location['state']] = 
isset($totals[$location['state']]) 
? $totals[$location['state']] + 1 : 1; 
return $totals; 
});

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@DerekB_WI
Use an outside variable
$searchWord = 'Bridge';

$placesWithBridges = array_ﬁlter($placesArray, 
function($location) use($searchWord) { 
return strpos($location['name'], $searchWord); 
});

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@DerekB_WI
Patterns
ApiPlacesController extends AbstractController {

…

}

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@DerekB_WI
Patterns
/** 
* route - /api/place 
*/

public function allPlaces() { 
$places = $this->repository->retrieveAll();  
$placesDtos = array_map( 
return PlacesTransformer::toDTO($place); 
}, $places);

return convertToJson($placesDtos);

}

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@DerekB_WI
Patterns
/** 
* route - /api/user/$userId/place 
*/

public function placesByUser($userId) { 
$places = $this->repository->retrieveAll();  
$placesDtos = array_map( 
return PlacesTransformer::toDTO($place); 
}, array_ﬁlter($places, function($place) { 
return LegacyMiddleware::shouldInclude($place); 
} 
));

return convertToJson($placesDtos); 
}

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@DerekB_WI
Immutable
$searchWord = 'Bridge';

$placesWithBridges = array_ﬁlter($placesArray, 
function($location) use($searchWord) {

$searchWord = ‘something else’; 
return strpos($location['name'], $searchWord); 
});

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@DerekB_WI
Mutable
array_walk( 
$placesArray, 
function(&$location, $key) { 
$location['distance'] = calcDistance($location); 
});

array_multisort( 
array_column($placesArray, 'distance'), 
SORT_ASC, 
$placesArray);

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@DerekB_WI
Generators
function location_file_generator($filename) 
{ 
$file = fopen($filename, 'r');

while(($fileData = fgetcsv($file, 1000, "\t")) !== FALSE) {
yield $fileData; 
} 
}

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@DerekB_WI
Generators
 
foreach(location_ﬁle_generator($ﬁlename) as $line)  
{ 
... 
}

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@DerekB_WI
Generators
• Pro: Reduced Memory Usage

• Pro: Easy syntax

• Con: Cannot use array functions

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@DerekB_WI
Generator Map
function map(Traversable $data, Callable $func) {

foreach($data as $item) { 
yield call_user_func($func, $item); 
} 
}

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@DerekB_WI
Generator Map
foreach(map(location_ﬁle_generator($ﬁlename),  
function($item) { 
return $item[1]; 
}) as $line) {

…

}

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@DerekB_WI
Generator Filter
function ﬁlter(Traversable $data, Callable $func) {

foreach($data as $item) { 
if (call_user_func($func)) { 
yield $item; 
} 
} 
}

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@DerekB_WI
Generator Filter
foreach(filter(location_file_generator($filename),  
function($item) { 
return $item[1] == 1; 
}) as $line) {

…

}

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@DerekB_WI
Data Structures
• Standard PHP Library - SPL

• Common Structures - widely used in other languages

• Many have ﬁlter and reduce functions

• apt install php-ds

• pecl install ds

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@DerekB_WI
Hash Map
$map = new DS\Map(); 
$map->put('AK', PlaceFactory::make('Alaska')); 
$map->put('WI', PlaceFactory::make('Wisconsin'));

$map->ﬁlter(function($key, $value) { 
return $value->population > 5000000; 
});

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@DerekB_WI
Hash Map
$map = new DS\Map(); 
$map->put('AK', PlaceFactory::make('Alaska')); 
$map->put('WI', PlaceFactory::make('Wisconsin'));

$map->reduce(function($carry, $key, $value) { 
return $carry + $value->population; 
}, 0);

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@DerekB_WI
Iterators
class MyIter implements Iterator { 
protected $data; 
protected $index; 
protected $valid = true;

…

}

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@DerekB_WI
Iterators
public function __construct($inArray) { 
$this->data = $inArray; 
$this->index; 
}

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@DerekB_WI
Iterators
public function current() { 
return $this->data[$this->index]; 
}

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@DerekB_WI
Iterators
public function next() { 
$this->index++;

if ($this->index >= count($this->data)) { 
$this->valid = false; 
return null; 
}

return $this->current();

}

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@DerekB_WI
Iterators
public function key() { 
return $this->index; 
}

public function valid() { 
return $this->valid; 
}

public function rewind() { 
$this->index = 0; 
}

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@DerekB_WI
Invoke Iterator
foreach(new MyIter($someArray) as $it) { 
… 
}

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@DerekB_WI
Invoke Iterator + Map
foreach(map(new MyIter($someArray), function($item) { 
… 
}) as $it) { 
… 
}

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@DerekB_WI
Laravel Collections

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@DerekB_WI
CakePHP MapReduce

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@DerekB_WI
Doctrine Collections

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@DerekB_WI
Async/Process
• Symfony process component

• Promise library

• Job Queues

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@DerekB_WI
Promise
use GuzzleHttp\Promise\Promise;

$promise = new Promise(function() { … });

$result = $promise->then( 
function($value) { 
// handle result 
} 
);

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@DerekB_WI
Resources
• https://www.newyorker.com/magazine/2018/12/10/the-friendship-that-made-google-huge

• https://static.googleusercontent.com/media/research.google.com/en//archive/mapreduce-osdi04.pdf

• https://medium.com/@oscarstiﬀelman/a-brief-history-of-mapreduce-97aec97df8ﬀ

• https://www.sitepoint.com/parallel-programming-pthreads-php-fundamentals/

• https://www.dragonbe.com/2015/07/speeding-up-database-calls-with-pdo-and.html

• https://github.com/doctrine/collections/blob/master/lib/Doctrine/Common/Collections/Collection.php

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Map, Filter, and Reduce in PHP

Map, Filter, and Reduce in PHP

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