Identifying duplicates in a column and summarize associated cells from another column

[Daxter]

I have a table of transactions with amounts, transaction IDs and customers where several transactions can have the same customer. I would like to identify the duplicates in the customer column, and summarize the amounts associated to each individual customer. From then, I would like to sort these sums in a column, with decreasing sums. Is there any way to make this happen with DAX-formulas?

[jthomson]

Why would you not just use a matrix?