SPL FilterIterator example

data.php

$items = array(
    array(
        'name' => 'Pants',
        'available' => 1,
        'sold' => 1,
    ),
    array(
        'name' => 'Shoes',
        'available' => 1,
        'sold' => 0,
    ),
);

functional.php

$available = __::select($items, function($item) {
    if (($item['available'] - $item['sold']) > 0) {
        return true;
    }

    return false;
});

functional2.php

$available = function($item) {
    if (($item['available'] - $item['sold']) > 0) {
        echo $item['name'], PHP_EOL;
    }
};

__::select($items, $available);

procedural.php

$available = array();

foreach ($items as $item) {
    if (($item['available'] - $item['sold']) > 0) {
        $available[] = $item;
    }
}

spl.php

class SellableItems extends FilterIterator
{
    public function accept()
    {
        $current = $this->current();

        if (($current['available'] - $current['soldout']) > 0) {
            return true;
        }

        return false;
    }
}

$available = new SellableItems(new ArrayIterator($items));