When working with data, you often need to know how many unique items you have in a list. For example, you might wish to know how many customers you have in your database, how many products you can offer to distributors, or all the countries or geographical regions you make sales in.
The required data is frequently stored in tables or lists where duplication is rife. Therefore, how do you “retire” the replicants? Here, I consider three approaches, reviewing the