A Creating Filemaker Pro summary reports--Tutorial can be set up to do this. A related table can also be used.
Using a summary report, you can set up a list view layout with no body part. Instead add a Sub Summary part, when sorted by customer to the layout and place customer name field in this part. A "count of" summary field can be defined and placed in this same part to report the number of records for each customer. Your records must be sorted by customer in order for this report to properly display the info.
In FileMaker 10 and newer, this report can be viewed in browse mode. In older versions, you have to switch to preview mode or print it.
If your list needs to be sorted by count, you'd need a related table of info where you have one record for each client. A calculation field using the count function (Count ( OrdersTable::OrderID ) ) can then compute the total orders per client. This approach will allow you to sort by count and can include the names of clients have not placed any orders.
Many thanks for this - have implemented the first part and got that working fine. Will have a play with creating the table so as to be able to sort the results by count over the next few days.
If you need option 2, then you don't have to create a summary report layout at all. They are two different approaches that have nearly, but not quite, the same result.
Cheers - I tried the first option first as it was the easiest. Now I have also tried the second and got that working - the second is the mist useful as it allows me to sort them, but both gave me valuable experience in using FileMaker. Many thanks again.