sample.php

<?php 

		/**
		*	Group cart items by category, and calculate the total of each category ;)
		**/

		$cart = [
			[ "name" => "product A", "price" => 15, "qty" => 5, "category" => "category 1"],
			[ "name" => "product B", "price" => 20, "qty" => 4, "category" => "category 2"],
			[ "name" => "product C", "price" => 30, "qty" => 2, "category" => "category 1"],
		];
		
		$cartByCategory = [];

		foreach($cart as $item){
			$category = $item['category'];
			
			if(!isset($cartByCategory[$category])){
				$cartByCategory[$category] = ["total" => 0,"items" => []];
			}
			
			$cartByCategory[$category]["total"] += $item['price'] * $item['qty'];
			$cartByCategory[$category]["items"][]= $item;
		}