In my java project, the data source is from dynamic excel sheet and the data is being updated by now and then. One excel sheet is Customer Information, the other is Purchase Order. Based on the information given, how could I figure out the the group of Customers who have purchased the same product ? Database is not imployed in my project, and I would like work out this issue by java programming, and which looks like difficult for me. Suggestions or solutions on my issue will be highly appreciated!