Get Products from Categories (array)

[diseñoPRO]

Hi guys,

I have a little problem. I need get the products from array of categories. These was saved with a helper tree form. 

Then, i did this:

public function getProducts()
{
    $categories = unserialize(Configuration::get('EXAMPLE_CATEGORIES'));
    $output = array();

    foreach ($categories as $id_category) {
        $category = new Category($id_category, $this->context->language->id);
        $products = $category->getProducts($this->context->language->id, 0, 10000);
        $output = array_merge($output, $products);
    }

    return $output;
}

This works but this return duplicate products, because some products exist in several different categories or parent/child. Have an idea or be better with an sql query?

Sorry for my English.
Please, help me!
Thanks.

Edited April 24, 2018 by diseñoPRO
... (see edit history)

[jgamio]

You just need to check if the product is on the $output  before add it to dont get duplicate products