Creating Attribute
If the attribute according to which the cart has to be split does not exist the admin can create the attribute.

On Magento admin panel Catalog > Attributes > Manage Attributes. Provide all the details related to the attribute and save the changes.

Assign the created attribute to a group
Once the attribute is created it has to be assigned to a group. On Magento admin panel, Catalog > Attributes > Manage Attribute Sets. Move the attribute from unassigned attributes to the group it needs to be set and click on save attribute set.

Enable the Extension
Once these settings are done, let us enable and set other settings required for the extension to function. Let’s suppose the changes for the extension is as per the screenshot below.

Assigning the attribute to products
Product User1, User3 has the attribute warehouse and User3 does not have this attribute.

User1

User2

User3

Add products to the cart
Let add the products to the cart. Click on the view shopping cart to view the complete details of the cart.

As the product User1 and User3 has warehouse attribute it is clubbed in one cart and the product User2 did not have the warehouse attribute it is in a different cart.

Now here the customers get a choice to decide if wants to proceed with checkout for both cart or just one of them. When the customer clicks on proceed to checkout, on shipping method page all the shipping method which was set at the backend will be available. Like in this example we have set Free Shipping as shipping method allowed.

Click on continue, the next page will be of payment information. Here the customer will get the list of payment method which was saved at the admin side. In this example, we have added cash on delivery and check/ money order as the payment methods allowed for the customers.

Click on continue, in order review page the customer will get the complete information about the items in the cart and which he opt to purchase.

Click on place order, the order gets placed having two items in the cart.