Adding a group by clause to PXProcessingJoin

Hi,
 

I am creating a new processing screen and have created the DataView below to grab the data I need for the processing grid.
 

public PXProcessingJoin<ARInvoice,
        InnerJoin<Customer, On<ARInvoice.customerID, Equal<Customer.bAccountID>>>,
        Where<ARInvoice.customerID, IsNotNull>,
        OrderBy<Asc<ARInvoice.customerID>>>
        Invoices; 

At the moment it is returning multiple rows for the same customer, as it is returning each invoice, but I would like the query to group on ARInvoice.CustomerID so that I can see which customers have overdue invoices.

The reason for this is I want the processing screen to send email reminders for overdue invoices, and I only want one email sent per customer, rather than an email per invoice.

Is there a way I can include this clause into the above query?

Let me know if you need any other information.

Kind regards,

Andrew