Reduces the set to a single value using a callback function

# Ds\Set::reduce

(PECL ds >= 1.0.0)

Ds\Set::reduce — Reduces the set to a single value using a callback function

### 説明

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

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

### パラメータ

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

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

  `value`

    The value of the current iteration.

`initial`

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

### 返り値

The return value of the final callback.

### 例

例1 Ds\Set::reduce() with initial value example

`<?php
$set = new \Ds\Set([1, 2, 3]);
$callback = function($carry, $value) {
return $carry * $value;
};
var_dump($set->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\Set::reduce() without an initial value example

`<?php
$set = new \Ds\Set([1, 2, 3]);
var_dump($set->reduce(function($carry, $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)