Reduces the map to a single value using a callback function

说明

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

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

参数

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.

返回值

The return value of the final callback.

范例

示例 #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
?>

以上例程的输出类似于：

int(30)

示例 #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
?>

以上例程的输出类似于：

int(21)