php

Generator vs array_map

Remy Honig bio photo By Remy Honig Comment

Introduction

I never liked the syntax of array_map but generator support in php 5.5 makes mapping a little bit more readable and much more memory-efficient.

With array map

$numbers = [1, 2, 3];

$result = array_map(
    function($i) {
        return $i = $i + 1;
    },
    $numbers
);

print_r($result);

Array
(
    [0] => 2
    [1] => 3
    [2] => 4
)

Note that the $result array contains the entire mapped result. This is different with generators as you will see in the next block.

With generator

function increaseByOne($numbers) {
    foreach ($numbers as $number) {
        yield $number + 1;
    }
}

print_r(iterator_to_array(
    increaseByOne([1, 2, 3])
));

Array
(
    [0] => 2
    [1] => 3
    [2] => 4
)

The generator function increaseByOne has to be looped to get any results as it is processes the input array one element at a time. The array_map function will return the whole mapped array.

With nested array maps

Option 1

$numbers = [1, 2, 3];

$result = array_map(
    function($j) {
        return $j * 2;
    },
    array_map(
        function($i) {
            return $i = $i + 1;
        },
        $numbers
    )
);

print_r($result);

Array
(
    [0] => 4
    [1] => 6
    [2] => 8
)

Option 2

function increaseByOne($numbers) {
    return array_map(
        function($i) {
            return $i = $i + 1;
        },
        $numbers
    );
}

function multiplyByTwo($numbers) {
    return array_map(
        function($j) {
            return $j * 2;
        },
        $numbers
    );
}

print_r(multiplyByTwo(increaseByOne([1, 2, 3])));

Array
(
    [0] => 4
    [1] => 6
    [2] => 8
)

With nested generators

function increaseByOne($numbers) {
    foreach ($numbers as $number) {
        yield $number + 1;
    }
}

function multiplyByTwo($numbers) {
    foreach ($numbers as $number) {
        yield $number * 2;
    }
}

print_r(iterator_to_array(
    multiplyByTwo(increaseByOne([1, 2, 3]))
));

Array
(
    [0] => 4
    [1] => 6
    [2] => 8
)