PHP Manual: Reduces the sequence to a single value using a callback function

Description

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

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

Parameters

callback

mixed callback(mixed $carry, mixed $value)

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.

Return Values

The return value of the final callback.

Examples

Example #1 Ds\Sequence::reduce with initial value example

<?php
$sequence = new \Ds\Vector([1, 2, 3]);

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

var_dump($sequence->reduce($callback, 5));

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

The above example will output something similar to:

int(30)

Example #2 Ds\Sequence::reduce without an initial value example

<?php
$sequence = new \Ds\Vector([1, 2, 3]);

var_dump($sequence->reduce(function($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
?>

The above example will output something similar to:

int(21)