Splitting of entity (products, categories etc.) collections into some equal parts?

Question

does anyone have an idea, how can I split one collection of entities in Magento into three equal independent collections?

Following example:

$_category = Mage::getModel('catalog/category')->load(129);
$_category_children = $_category->getChildrenCategories();

In $_category_children I have a collection of subcategories of the category with ID=129. Let's say, there are 30 subcategories there. Now I want to get three collections of it:

$_category_children_1 -> independent collection with items 1-10 of $_category_children
$_category_children_2 -> independent collection with items 11-20 of $_category_children
$_category_children_3 -> independent collection with items 21-30 of $_category_children

I already tried http://php.net/manual/function.array-chunk.php, but it doesn't help, but only returns NULL.

Thanks a lot in advance for the help!

Answer 1

Call category collection and create different collection on limit

$_category = Mage::getModel('catalog/category')->load(129);

    $Children=$_category->getResource()->getChildren($_category, false));
            $collection = Mage::getResourceModel('catalog/product_collection');
            $collection->addAttributeToSelect('url_key')
                ->addAttributeToSelect('name')
                ->addAttributeToSelect('all_children')
                ->addAttributeToSelect('is_anchor')
                ->setOrder('position', Varien_Db_Select::SQL_ASC)
                ->joinUrlRewrite()
            ->addAttributeToFilter('is_active', 1)
                ->addIdFilter( implode(',', $Children))
                ->addAttributeToSelect('*');

Using setCurPage() and setPageSize() divide the collection by three part

Collection for 1-10;

$collection->setCurPage(1);
$collection->setPageSize(10);

Collection for 11-20;

$collection->setCurPage(2);
$collection->setPageSize(10);

Collection for 21-30;

$collection->setCurPage(3);
$collection->setPageSize(10)

;

Answer 2

Thank you very much for the feedback! Now I think, I found the solution. My final code is:

$parent_category_id = $this->getData('parent_category_id'); // 129
$number_of_columns = $this->getData('number_of_columns');   // 3

/** @var $_category Mage_Catalog_Model_Resource_Category_Collection */
$_categories = Mage::getModel('catalog/resource_category_collection')
    ->addAttributeToSort('name', 'ASC')
    ->addAttributeToSelect(array('name', 'url'))
    ->addIsActiveFilter()
    ->addFieldToFilter('parent_id', $parent_category_id);

$_page_size = (int) round($_categories->getSize() / $number_of_columns);

$_categories1 = clone $_categories;
$_categories1 = $_categories1->setPageSize(10)->setCurPage(1);
$_categories2 = clone $_categories;
$_categories2 = $_categories2->setPageSize(10)->setCurPage(2);
$_categories3 = clone $_categories;
$_categories3 = $_categories3->setPageSize(10)->setCurPage(3);

And then I can iterate through them separately:

<div class="column even" style="width: 25% !important;">
    <div class="itemMenu level1">
        <div class="title"><strong>Alphabetisch:</strong></div>
        <?php foreach ($_categories1 as $_child): ?>
        <a class="itemMenuName level1" href="<?php echo $_child->getUrl() ?>">
            <span><?php echo $_child->getName() ?></span>
        </a>
        <?php endforeach; ?>
    </div>
</div>

<div class="column odd" style="width: 25% !important; margin-top:2.75em;">
    <div class="itemMenu level1">
        <?php foreach ($_categories2 as $_child): ?>
        <a class="itemMenuName level1" href="<?php echo $_child->getUrl() ?>">
            <span><?php echo $_child->getName() ?></span>
        </a>
        <?php endforeach; ?>
    </div>
</div>

<div class="column even" style="width: 25% !important; margin-top:2.75em;">
    <div class="itemMenu level1">
        <?php foreach ($_categories3 as $_child): ?>
        <a class="itemMenuName level1" href="<?php echo $_child->getUrl() ?>">
            <span><?php echo $_child->getName() ?></span>
        </a>
        <?php endforeach; ?>
    </div>
</div>


<div class="clearBoth"></div>

I'm aware of the increase of memory consumption through clone, but hope, that there will be no other negative performance impacts. If you see any drawbacks for the solution, please, don't hesitate to post / ask.

Answer 3

@Amit has a good answer.

Another way is to use PHP's array_chunk. That way you only do one SQL query instead of three.

You can use it like so:

$_categoryChuncks = array_chunk(
    $_category->getChildrenCategories()->getItems(),
    ceil($_count / 3)
);

Note: I think when flat categories are enabled, $_category->getChildrenCategories() returns an array, not a collection model, so you might have to check for that.