Re: [rules-users] Grouping and Aggregation in Drools

Thanks for the quick response Wolfgang. Appreciate it. I have a question about this line in the rule you specified below   not Category( $sup == name, cart == $cart ) What should this name be ? How will this be determined at runtime ? Also would you mind how these rules work . I tried to implement it but could not make much progress. On the other hand i tried with a slightly different approach. My use-case is the Customer will have an actual cart and a suggested cart when they are made available in the working memory. Here's the rule : - rule "Test 1" when  Customer ($actual_cart : actual_cart, $reference_cart : reference_cart)  $item : CartItem () from $actual_cart  $category_limit : Category (category == $item.category, $limit : categoryLimit) from $reference_cart    // This will accumulate as many times as the category exists in the actual_cart  $total : Double()     from accumulate ( CartItem (category == $item.category, $value : actual_value) from $actual_cart,          sum ($value)              )  //if there's no row in the reference_Cart for specified category then $limit should be set to zero.  eval ($total >  $limit)          then  //record the category where the excess items has been purchased end There are some obvious issues with the approach that i have outlined above. Wonder if there's some way to get around them. Regards, Manav ----- Original Message ---- From: Wolfgang Laun <wolfgang.laun(a)gmail.com&gt; To: Manav <manav7574(a)yahoo.com>; Rules Users List <rules-users(a)lists.jboss.org&gt; Sent: Sat, January 8, 2011 3:09:12 PM Subject: Re: [rules-users] Grouping and Aggregation in Drools A Category combines a name, a reference to the cart, a sum of article values and a percentage. Any change in the cart triggers an update of all associated Category facts. The rules are quite simple. The update of the cart (not shown here) must be run with higher salience. rule "first super"   $cart. Cart( $tot: total )   $art: Article( $cart: cart, $val: value, $sup. super, $sub: sub )   not Category( $sup == name, cart == $cart ) then   insert( new Category( $sup, $car, $val, $val/$tot ) ); end rule "next super"   $cart. Cart( $tot: total )   $art: Article( $cart: cart, $val: value, $sup. super, $sub: sub )   $cat: Category( $sup == name, cart == $cart ) then   Double newVal =$cat.getValue() + $val;   modify( $cat ){     setValue( newVal ),     setPercent( newVal / tot )   } end Almost identical rules handle sub-categories. For removal from the cart, you can use the same rule if the article value is negative. Make sure to avoid division by 0 if the last item is removed from the cart. The reference cart is similar in structure, and the comparison rule is generic for all categories. -W On 08/01/2011, Manav <manav7574(a)yahoo.com&gt; wrote: