How to get category ids from product collection

Question

I have an array of product ids now i want to get all categories where these products belongs in magento2.

For example

we have categories cat_1, cat_2 ,cat_3, cat_4, cat_5, cat_6, cat_7

product_id_1 exist in cat_1, cat_2

product_id_2 exist in cat_3, cat_4

product_id_3 exist in cat_1, cat_5

Now i want a collection of category having categories cat1, cat_2, cat_3, and cat_5

Answer 1

You can use array_merge to get all the ids from collection

$prodIds=$block->getProductCollection();
$catIds=[];         
foreach($prodIds as $pid){          
    $product = $this->_productloader->create()->load($pid);   
    $proCats = $product->getCategoryIds();    
    $catIds= array_merge($catIds, $pproCats);   
}

$finalCat = array_unique($catIds);

Answer 2

If you want to get all category ids based on the array of your product ids. You can get it as following way

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$productIdsArray = array(1,2,3,4,5,6,7,8,9); // your product ids
$products = $objectManager->create("Magento\Catalog\Model\Product")->getCollection()->addAttributeToFilter('entity_id',array('in'=> $productIdsArray));

$allCategories = array();  // create a blank array
foreach ($products as $product) {
    $allCategories = array_merge($allCategories, $product->getCategoryIds());  // Merge product category ids array with $allCategories
}
$finalArray = array_unique($allCategories); // removes duplicate entries from an array

Note: Do not use ObjectManger directly in your phtml file. I recommend to use dependency injection.

Answer 3

You can always get the assigned categories of a product using following code.

In Constructor:

public function __construct(
        ...
        \Magento\Catalog\Model\ProductFactory $productFactory
    ) {
        ...
        $this->_productFactory = $productFactory;
        ...
    }

And in your method use following code

$product = $this->_productFactory->create()->load($pid); // $pid = Product_ID

$cats = $product->getCategoryIds(); // All Categories of $product you will get in array format eg. array(catid 1, catid 2, catid 3)

Answer 4

You can get collection of category by Id in block like this:

namespace Your\Modules\Block;


protected $_categoryFactory;

public function __construct(
...
\Magento\Catalog\Model\CategoryFactory $categoryFactory,
...
)
{
...
$this->_categoryFactory = $categoryFactory;
...
}
public function getCategory($categoryId)
{
    $category = $this->_categoryFactory->create();
    $category->load($categoryId);
    return $category;
}
public function getProductbyCategory($categoryId) 
{
    $products = $this->getCategory($categoryId)->getProductCollection();
    $products->addAttributeToSelect('*');
    return $products;
}

Call function in your phtml file:

$collection = $block->getProductbyCategory($catId);
foreach($collection as $data){
    $data->getTitle();
}

Or you can define same like that in your helper and then call in phtml:

$yourHelper = $this->helper('Your\Module\Helper\Data');
$collection = $yourHelper->getProductbyCategory($catId);
foreach($collection as $data){
        $data->getTitle();
    }

Hope this help.