Ds\Map::reduce

(PECL ds >= 1.0.0)

Ds\Map::reduce — Reduces the map to a single value using a callback function

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public Ds\Map::reduce ( callable $callback [, mixed $initial ] ) : mixed

Reduces the map to a single value using a callback function.

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callback
callback ( mixed $carry , mixed $key , mixed $value ) : mixed
carry

The return value of the previous callback, or initial if it's the first iteration.

key

The key of the current iteration.

value

The value of the current iteration.

initial

The initial value of the carry value. Can be NULL.

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The return value of the final callback.

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Example #1 Ds\Map::reduce() with initial value example

<?php
$map = new \Ds\Map(["a" => 1, "b" => 2, "c" => 3]);

$callback = function($carry, $key, $value) {
    return $carry * $value;
};

var_dump($map->reduce($callback, 5));

// Iterations:
//
// $carry = $initial = 5
//
// $carry = $carry * 1 =  5
// $carry = $carry * 2 = 10
// $carry = $carry * 3 = 30
?>

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int(30)

Example #2 Ds\Map::reduce() without an initial value example

<?php
$map = new \Ds\Map(["a" => 1, "b" => 2, "c" => 3]);

var_dump($map->reduce(function($carry, $key, $value) {
    return $carry + $value + 5;
}));

// Iterations:
//
// $carry = $initial = null
//
// $carry = $carry + 1 + 5 =  6
// $carry = $carry + 2 + 5 = 13
// $carry = $carry + 3 + 5 = 21
?>

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int(21)