PHP マニュアル: Reduces the map to a single value using a callback function

説明

public mixed Ds\Map::reduce(callable $callback, mixed $initial = ?)

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

パラメータ

callback

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

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.

戻り値

The return value of the final callback.

例

例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
?>

上の例の出力は、たとえば以下のようになります。

int(30)

例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
?>

上の例の出力は、たとえば以下のようになります。

int(21)