src/Zicht/Itertools/twig/Extension.php
public function reduce($iterable, $closure = 'add', $initializer = null)
    {
        return Itertools\reduce($iterable, $closure, $initializer);
    }
public function reduce($iterable, $closure = 'add', $initializer = null)
    {
        return Itertools\reduce($iterable, $closure, $initializer);
    }
Reduce an iterable to a single value

Simple examples:
{{ [1,2,3]|reduce }} --> 6
{{ [1,2,3]|reduce('max') }} --> 3

Sro example to get the prices for all items in the basket:
{{ transaction_snapshot.Basket.Items|map('TotalPrice.Amount')|reduce }}

@param array|string|\Iterator $iterable
@param string|\Closure $closure
@param mixed $initializer
@return mixed